diff --git a/.eslintrc.json b/.eslintrc.json
index 9d8ed29..87bad29 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -10,6 +10,9 @@
     "no-shadow": ["error", { "allow": ["err"] }],
     "handle-callback-err": "error",
     "prefer-arrow-callback": "error",
-    "curly": ["error", "multi", "consistent"]
+    "curly": ["error", "multi-or-nest", "consistent"],
+    "consistent-return": ["error", {"treatUndefinedAsUnspecified": true}],
+    "no-buffer-constructor": "error",
+    "prefer-const": ["error", {"destructuring": "all"}]
   }
 }
diff --git a/client/app.js b/client/app.js
index fe5e468..f6ca4b3 100644
--- a/client/app.js
+++ b/client/app.js
@@ -51,14 +51,14 @@ function pagify(pageName, page) {
     if (!page.init) {
       state = null;
       fulfill();
-      return;
+      return null;
     }
 
     return new Promise(resolve => {
       page
         .init(args)
         .then(st => {
-          if (!st) return m.route.set("/");
+          if (!st) return void m.route.set("/");
           state = st;
           resolve();
           fulfill();
diff --git a/client/autocomplete-compnent.js b/client/autocomplete-compnent.js
index d4cb437..c2b2e4b 100644
--- a/client/autocomplete-compnent.js
+++ b/client/autocomplete-compnent.js
@@ -20,7 +20,7 @@ class Autocomplete {
 
     el.addEventListener("focus", () => {
       this.element = el;
-      let domRect = el.getBoundingClientRect();
+      const domRect = el.getBoundingClientRect();
       this.container.style.left = `${domRect.left}px`;
       this.container.style.width = `${domRect.width}px`;
       this.container.style.top = `${domRect.bottom}px`;
@@ -36,13 +36,15 @@ class Autocomplete {
 
     el.addEventListener("keydown", e => {
       if (this.element !== el) return;
-      if (e.key === "Escape") this.hide();
-      else if (e.key === "Enter")
+      if (e.key === "Escape") {
+        this.hide();
+      } else if (e.key === "Enter") {
         if (this.default != null) {
           el.value = this.default;
           e.preventDefault();
           this.update();
         }
+      }
     });
 
     el.addEventListener("input", () => {
@@ -94,10 +96,10 @@ class Autocomplete {
 
       this.default = suggestions[0];
 
-      for (let suggestion of suggestions) {
-        let e = document.createElement("div");
+      for (const suggestion of suggestions) {
+        const e = document.createElement("div");
         e.className = "suggestion";
-        let t = document.createTextNode(suggestion);
+        const t = document.createTextNode(suggestion);
         e.appendChild(t);
         e.addEventListener("mousedown", ev => {
           ev.preventDefault();
diff --git a/client/components/all-parameters.js b/client/components/all-parameters.js
index 4c5e6e9..8ed6ce7 100644
--- a/client/components/all-parameters.js
+++ b/client/components/all-parameters.js
@@ -12,7 +12,7 @@ const component = {
   view: vnode => {
     const device = vnode.attrs.device;
 
-    let search = m("input", {
+    const search = m("input", {
       type: "text",
       placeholder: "Search parameters",
       oninput: e => {
@@ -20,10 +20,10 @@ const component = {
       }
     });
 
-    let instanceRegex = /\.[0-9]+$/;
+    const instanceRegex = /\.[0-9]+$/;
     let re;
     if (vnode.state.searchString) {
-      let keywords = vnode.state.searchString.split(" ").filter(s => s);
+      const keywords = vnode.state.searchString.split(" ").filter(s => s);
       if (keywords.length)
         re = new RegExp(keywords.map(s => escapeRegExp(s)).join(".*"), "i");
     }
@@ -31,22 +31,22 @@ const component = {
     const rows = Object.keys(device)
       .sort()
       .map(k => {
-        let p = device[k];
-        let val = [];
-        let attrs = {};
+        const p = device[k];
+        const val = [];
+        const attrs = {};
         if (re) {
-          let str = p.value && p.value[0] ? `${k} ${p.value[0]}` : k;
+          const str = p.value && p.value[0] ? `${k} ${p.value[0]}` : k;
           if (!re.test(str)) attrs.style = "display: none;";
         }
 
-        if (p.object === false)
+        if (p.object === false) {
           val.push(
             m(
               components.get("parameter"),
               Object.assign({ device: device, parameter: k })
             )
           );
-        else if (p.object && p.writable)
+        } else if (p.object && p.writable) {
           if (instanceRegex.test(k)) {
             val.push(
               m(
@@ -82,6 +82,7 @@ const component = {
               )
             );
           }
+        }
 
         val.push(
           m(
diff --git a/client/components/container.js b/client/components/container.js
index 9d1713a..600ac18 100644
--- a/client/components/container.js
+++ b/client/components/container.js
@@ -12,10 +12,10 @@ const component = {
   view: vnode => {
     if (vnode.attrs.filter) {
       const filter = memoizedParse(vnode.attrs.filter);
-      if (!store.evaluateExpression(filter, vnode.attrs.device)) return;
+      if (!store.evaluateExpression(filter, vnode.attrs.device)) return null;
     }
 
-    let children = Object.values(vnode.attrs.components).map(c => {
+    const children = Object.values(vnode.attrs.components).map(c => {
       if (typeof c !== "object") return `${c}`;
       const attrs = Object.assign({}, vnode.attrs, c);
       return m(components.get(attrs.type), attrs);
diff --git a/client/components/device-faults.js b/client/components/device-faults.js
index 2eff14a..cd8c232 100644
--- a/client/components/device-faults.js
+++ b/client/components/device-faults.js
@@ -20,7 +20,7 @@ const component = {
     const thead = m("thead", m("tr", headers));
 
     const rows = [];
-    for (let f of faults.value)
+    for (const f of faults.value) {
       rows.push([
         m("td", f["channel"]),
         m("td", f["code"]),
@@ -51,14 +51,17 @@ const component = {
           )
         )
       ]);
+    }
 
     let tbody;
-    if (rows.length) tbody = m("tbody", rows.map(r => m("tr", r)));
-    else
+    if (rows.length) {
+      tbody = m("tbody", rows.map(r => m("tr", r)));
+    } else {
       tbody = m(
         "tbody",
         m("tr.empty", m("td", { colspan: headers.length }, "No faults"))
       );
+    }
 
     return m("table.table", thead, tbody);
   }
diff --git a/client/components/overview-dot.js b/client/components/overview-dot.js
index 6789df4..71fc0d8 100644
--- a/client/components/overview-dot.js
+++ b/client/components/overview-dot.js
@@ -14,7 +14,7 @@ const component = {
   view: vnode => {
     const device = vnode.attrs.device;
     const chart = CHARTS[vnode.attrs.chart];
-    for (let slice of Object.values(chart.slices)) {
+    for (const slice of Object.values(chart.slices)) {
       const filter = memoizedParse(slice.filter);
       if (store.evaluateExpression(filter, device)) {
         const dot = m(
@@ -35,6 +35,7 @@ const component = {
         return m("span.overview-dot", dot, `${slice.label}`);
       }
     }
+    return null;
   }
 };
 
diff --git a/client/components/parameter-table.js b/client/components/parameter-table.js
index f406b8a..947ebbb 100644
--- a/client/components/parameter-table.js
+++ b/client/components/parameter-table.js
@@ -9,7 +9,7 @@ import * as expressionParser from "../../common/expression-parser";
 
 const component = {
   oninit: vnode => {
-    let obj = expression.parse(vnode.attrs.parameter);
+    const obj = expression.parse(vnode.attrs.parameter);
     if (!Array.isArray(obj) || !obj[0] === "PARAM")
       throw new Error("Object must be a parameter path");
     vnode.state.object = obj[1];
@@ -30,19 +30,20 @@ const component = {
 
     const instances = new Set();
     const prefix = `${object}.`;
-    for (let p in device)
+    for (const p in device) {
       if (p.startsWith(prefix)) {
-        let i = p.indexOf(".", prefix.length);
+        const i = p.indexOf(".", prefix.length);
         if (i === -1) instances.add(p);
         else instances.add(p.slice(0, i));
       }
+    }
 
     const headers = Object.values(parameters).map(p => m("th", p.label));
 
     const thead = m("thead", m("tr", headers));
 
     const rows = [];
-    for (let i of instances) {
+    for (const i of instances) {
       const row = parameters.map(p => {
         const param = expressionParser.map(p.parameter, e => {
           if (Array.isArray(e) && e[0] === "PARAM")
@@ -62,7 +63,7 @@ const component = {
         );
       });
 
-      if (device[i].writable === true)
+      if (device[i].writable === true) {
         row.push(
           m(
             "td",
@@ -82,15 +83,17 @@ const component = {
             )
           )
         );
+      }
       rows.push(m("tr", row));
     }
 
-    if (!rows.length)
+    if (!rows.length) {
       rows.push(
         m("tr.empty", m("td", { colspan: headers.length }, "No instances"))
       );
+    }
 
-    if (device[object].writable === true)
+    if (device[object].writable === true) {
       rows.push(
         m(
           "tr",
@@ -114,6 +117,7 @@ const component = {
           )
         )
       );
+    }
 
     let label;
     if (vnode.attrs.label) label = m("h2", vnode.attrs.label);
diff --git a/client/components/parameter.js b/client/components/parameter.js
index 1cae675..03d515d 100644
--- a/client/components/parameter.js
+++ b/client/components/parameter.js
@@ -11,27 +11,22 @@ const memoizedParse = memoize(expression.parse);
 
 const evaluateParam = memoize((exp, obj, now) => {
   let timestamp = now;
-  let params = new Set();
-  let value = expression.evaluate(
-    memoizedParse(exp),
-    obj,
-    now,
-    e => {
-      if (Array.isArray(e)) {
-        if (e[0] === "PARAM") {
-          params.add(e[1]);
-          if (!Array.isArray(e[1])) {
-            let p = obj[e[1]];
-            if (p && p.valueTimestamp)
-              timestamp = Math.min(timestamp, p.valueTimestamp);
-          }
+  const params = new Set();
+  const value = expression.evaluate(memoizedParse(exp), obj, now, e => {
+    if (Array.isArray(e)) {
+      if (e[0] === "PARAM") {
+        params.add(e[1]);
+        if (!Array.isArray(e[1])) {
+          const p = obj[e[1]];
+          if (p && p.valueTimestamp)
+            timestamp = Math.min(timestamp, p.valueTimestamp);
         }
-        if (e[0] === "FUNC" && e[1] === "DATE_STRING" && !Array.isArray(e[2]))
-          return new Date(e[2]).toLocaleString();
       }
-      return e;
+      if (e[0] === "FUNC" && e[1] === "DATE_STRING" && !Array.isArray(e[2]))
+        return new Date(e[2]).toLocaleString();
     }
-  );
+    return e;
+  });
 
   let parameter = params.size === 1 ? params.values().next().value : null;
   if (Array.isArray(parameter)) parameter = null;
@@ -42,7 +37,7 @@ const component = {
   view: vnode => {
     const device = vnode.attrs.device;
 
-    let { value, timestamp, parameter } = evaluateParam(
+    const { value, timestamp, parameter } = evaluateParam(
       vnode.attrs.parameter,
       vnode.attrs.device,
       store.getTimestamp()
@@ -51,7 +46,7 @@ const component = {
     if (value == null) return null;
 
     let edit;
-    if (device[parameter] && device[parameter].writable)
+    if (device[parameter] && device[parameter].writable) {
       edit = m(
         "button",
         {
@@ -72,6 +67,7 @@ const component = {
         },
         "✎"
       );
+    }
 
     return m(
       "span.parameter-value",
diff --git a/client/components/ping.js b/client/components/ping.js
index 89facae..93146c5 100644
--- a/client/components/ping.js
+++ b/client/components/ping.js
@@ -13,7 +13,7 @@ const component = {
     vnode.state.timeout = null;
   },
   view: vnode => {
-    let refresh = () => {
+    const refresh = () => {
       const device = vnode.attrs.device;
       let param =
         device["InternetGatewayDevice.ManagementServer.ConnectionRequestURL"];
@@ -34,20 +34,22 @@ const component = {
         });
     };
 
-    let t = vnode.state.timestamp + REFRESH_INTERVAL - Date.now();
+    const t = vnode.state.timestamp + REFRESH_INTERVAL - Date.now();
     clearTimeout(vnode.state.timeout);
     if (t <= 0) refresh();
     else vnode.state.timeout = setTimeout(refresh, t);
 
     if (vnode.state.host) {
       let status = "";
-      if (vnode.state.ping)
+      if (vnode.state.ping) {
         if (vnode.state.ping.avg != null)
           status = `${Math.trunc(vnode.state.ping.avg)} ms`;
         else status = "Unreachable";
+      }
 
       return m("div", `Pinging ${vnode.state.host}: ${status}`);
     }
+    return null;
   }
 };
 
diff --git a/client/components/put-form.js b/client/components/put-form.js
index e61127e..fb6a0de 100644
--- a/client/components/put-form.js
+++ b/client/components/put-form.js
@@ -12,8 +12,8 @@ const singular = {
 
 function createField(current, attr, focus) {
   if (attr.type === "combo") {
-    let options = [m("option", { value: "" }, "--Please choose--")];
-    for (let op of attr.options) options.push(m("option", { value: op }, op));
+    const options = [m("option", { value: "" }, "--Please choose--")];
+    for (const op of attr.options) options.push(m("option", { value: op }, op));
 
     let selected = "";
     if (attr.options.includes(current.object[attr.id]))
@@ -40,7 +40,7 @@ function createField(current, attr, focus) {
       name: attr.id,
       value: current.object[attr.id],
       oncreate: _vnode => {
-        let editor = codeMirror.fromTextArea(_vnode.dom, {
+        const editor = codeMirror.fromTextArea(_vnode.dom, {
           mode: "javascript",
           lineNumbers: true
         });
@@ -87,21 +87,22 @@ function createField(current, attr, focus) {
 
 const component = {
   view: vnode => {
-    let actionHandler = vnode.attrs.actionHandler;
-    let attributes = vnode.attrs.attributes;
-    let resource = vnode.attrs.resource;
-    let base = vnode.attrs.base || {};
-    if (!vnode.state.current)
+    const actionHandler = vnode.attrs.actionHandler;
+    const attributes = vnode.attrs.attributes;
+    const resource = vnode.attrs.resource;
+    const base = vnode.attrs.base || {};
+    if (!vnode.state.current) {
       vnode.state.current = {
         isNew: !base["_id"],
         object: Object.assign({}, base)
       };
+    }
 
-    let current = vnode.state.current;
+    const current = vnode.state.current;
 
-    let form = [];
+    const form = [];
     let focused = false;
-    for (let attr of attributes) {
+    for (const attr of attributes) {
       let focus = false;
       if (!focused && (current.isNew || attr.id !== "_id"))
         focus = focused = true;
@@ -117,9 +118,9 @@ const component = {
     }
 
     const submit = m("button.primary", { type: "submit" }, "Save");
-    let buttons = [submit];
+    const buttons = [submit];
 
-    if (!current.isNew)
+    if (!current.isNew) {
       buttons.push(
         m(
           "button.primary",
@@ -135,10 +136,11 @@ const component = {
           "Delete"
         )
       );
+    }
 
     form.push(m(".actions-bar", buttons));
 
-    let children = [
+    const children = [
       m("h1", `${current.isNew ? "New" : "Editing"} ${singular[resource]}`),
       m(
         "form",
@@ -147,7 +149,7 @@ const component = {
             e.redraw = false;
             e.target.onsubmit = null;
             e.preventDefault();
-            for (let elem of e.target.elements) elem.disabled = true;
+            for (const elem of e.target.elements) elem.disabled = true;
             submit.dom.textContent = "Loading ...";
             actionHandler("save", current.object);
           }
diff --git a/client/components/summon-button.js b/client/components/summon-button.js
index 8afdc4b..f70854d 100644
--- a/client/components/summon-button.js
+++ b/client/components/summon-button.js
@@ -37,28 +37,29 @@ const component = {
             .commit(
               [task],
               (deviceId, err, connectionRequestStatus, tasks2) => {
-                if (err)
-                  return notifications.push(
-                    "error",
-                    `${deviceId}: ${err.message}`
-                  );
+                if (err) {
+                  notifications.push("error", `${deviceId}: ${err.message}`);
+                  return;
+                }
 
-                for (let t of tasks2)
+                for (const t of tasks2)
                   if (t.status === "stale") taskQueue.deleteTask(t);
 
-                if (connectionRequestStatus !== "OK")
+                if (connectionRequestStatus !== "OK") {
                   notifications.push(
                     "error",
                     `${deviceId}: ${connectionRequestStatus}`
                   );
-                else if (tasks2[0].status === "stale")
+                } else if (tasks2[0].status === "stale") {
                   notifications.push(
                     "error",
                     `${deviceId}: No contact from device`
                   );
-                else if (tasks2[0].status === "fault")
+                } else if (tasks2[0].status === "fault") {
                   notifications.push("error", `${deviceId}: Refresh faulted`);
-                else notifications.push("success", `${deviceId}: Summoned`);
+                } else {
+                  notifications.push("success", `${deviceId}: Summoned`);
+                }
               }
             )
             .then(() => {
diff --git a/client/components/tags.js b/client/components/tags.js
index 76bf2cf..7a12881 100644
--- a/client/components/tags.js
+++ b/client/components/tags.js
@@ -11,7 +11,7 @@ const component = {
     if (vnode.attrs.writable != null) writable = vnode.attrs.writable;
 
     const tags = [];
-    for (let p of Object.keys(device))
+    for (const p of Object.keys(device))
       if (p.startsWith("Tags.")) tags.push(p.slice(5));
 
     tags.sort();
diff --git a/client/device-page.js b/client/device-page.js
index 907c6cd..809c2c4 100644
--- a/client/device-page.js
+++ b/client/device-page.js
@@ -7,10 +7,11 @@ import * as store from "./store";
 import * as components from "./components";
 
 function init(args) {
-  if (!window.authorizer.hasAccess("devices", 2))
+  if (!window.authorizer.hasAccess("devices", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   return Promise.resolve({
     deviceId: args.id,
@@ -22,15 +23,16 @@ const component = {
   view: vnode => {
     document.title = `${vnode.attrs.deviceId} - Devices - GenieACS`;
 
-    let dev = store.fetch("devices", vnode.attrs.deviceFilter).value;
+    const dev = store.fetch("devices", vnode.attrs.deviceFilter).value;
     if (!dev.length) return "Loading";
     const conf = config.ui.device;
     const cmps = [];
 
-    for (let c of Object.values(conf))
+    for (const c of Object.values(conf)) {
       cmps.push(
         m(components.get(c["type"]), Object.assign({ device: dev[0] }, c))
       );
+    }
 
     return [
       m("h1", vnode.attrs.deviceId),
diff --git a/client/devices-page.js b/client/devices-page.js
index 42d00d2..2eab86d 100644
--- a/client/devices-page.js
+++ b/client/devices-page.js
@@ -18,11 +18,9 @@ const PAGE_SIZE = config.ui.pageSize || 10;
 const memoizedParse = memoize(expression.parse);
 const memoizedJsonParse = memoize(JSON.parse);
 const memoizedGetSortable = memoize(str => {
-  let expressionParams = expression.extractParams(
-    expression.parse(str)
-  );
+  const expressionParams = expression.extractParams(expression.parse(str));
   if (expressionParams.length === 1) {
-    let param = expression.evaluate(expressionParams[0]);
+    const param = expression.evaluate(expressionParams[0]);
     if (typeof param === "string") return param;
   }
   return null;
@@ -52,7 +50,7 @@ const unpackSmartQuery = memoize(query => {
 function init(args) {
   return new Promise((resolve, reject) => {
     if (!window.authorizer.hasAccess("devices", 2))
-      return reject(new Error("You are not authorized to view this page"));
+      return void reject(new Error("You are not authorized to view this page"));
 
     const filter = args.filter;
     const sort = args.sort;
@@ -76,16 +74,17 @@ function renderTable(
     type: "checkbox",
     checked: devices.length && selected.size === devices.length,
     onchange: e => {
-      for (let d of devices)
+      for (const d of devices) {
         if (e.target.checked) selected.add(d["DeviceID.ID"].value[0]);
         else selected.delete(d["DeviceID.ID"].value[0]);
+      }
     },
     disabled: !total
   });
 
-  let labels = [m("th", selectAll)];
-  for (let param of parameters) {
-    let label = param.label;
+  const labels = [m("th", selectAll)];
+  for (const param of parameters) {
+    const label = param.label;
     let _param;
     if (!param.unsortable && (_param = memoizedGetSortable(param.parameter))) {
       let direction = 1;
@@ -94,7 +93,7 @@ function renderTable(
       if (sort[_param] > 0) symbol = "\u2bc6";
       else if (sort[_param] < 0) symbol = "\u2bc5";
 
-      let sortable = m(
+      const sortable = m(
         "button",
         {
           onclick: () => {
@@ -111,9 +110,9 @@ function renderTable(
     }
   }
 
-  let rows = [];
-  for (let device of devices) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const device of devices) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(device["DeviceID.ID"].value[0]),
       onchange: e => {
@@ -158,12 +157,13 @@ function renderTable(
     );
   }
 
-  if (!rows.length)
+  if (!rows.length) {
     rows.push(
       m("tr.empty", m("td", { colspan: parameters.length + 1 }, "No devices"))
     );
+  }
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null) footerElements.push(`${devices.length}/${total}`);
   else footerElements.push(`${devices.length}`);
 
@@ -179,12 +179,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -206,11 +207,12 @@ function renderActions(selected) {
         title: "Reboot selected devices",
         disabled: !selected.size,
         onclick: () => {
-          for (let d of selected)
+          for (const d of selected) {
             taskQueue.queueTask({
               name: "reboot",
               device: d
             });
+          }
         }
       },
       "Reboot"
@@ -224,11 +226,12 @@ function renderActions(selected) {
         title: "Factory reset selected devices",
         disabled: !selected.size,
         onclick: () => {
-          for (let d of selected)
+          for (const d of selected) {
             taskQueue.queueTask({
               name: "factoryReset",
               device: d
             });
+          }
         }
       },
       "Reset"
@@ -246,7 +249,7 @@ function renderActions(selected) {
           if (!confirm(`Deleting ${ids.length} devices. Are you sure?`)) return;
 
           let counter = 1;
-          for (let id of ids) {
+          for (const id of ids) {
             ++counter;
             store
               .deleteResource("devices", id)
@@ -278,7 +281,7 @@ function renderActions(selected) {
           if (!tag) return;
 
           let counter = 1;
-          for (let id of ids) {
+          for (const id of ids) {
             ++counter;
             store
               .updateTags(id, { [tag]: true })
@@ -312,7 +315,7 @@ function renderActions(selected) {
           if (!tag) return;
 
           let counter = 1;
-          for (let id of ids) {
+          for (const id of ids) {
             ++counter;
             store
               .updateTags(id, { [tag]: false })
@@ -345,13 +348,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/devices", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/devices", ops);
     }
@@ -360,17 +363,19 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let devs = store.fetch("devices", filter, {
+    const devs = store.fetch("devices", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
-    let count = store.count("devices", filter);
+    const count = store.count("devices", filter);
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let d of devs.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const d of devs.value) {
         if (vnode.state.selected.has(d["DeviceID.ID"].value[0]))
           selected.add(d["DeviceID.ID"].value[0]);
+      }
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(
diff --git a/client/drawer-component.js b/client/drawer-component.js
index 65b563a..45813d3 100644
--- a/client/drawer-component.js
+++ b/client/drawer-component.js
@@ -89,7 +89,7 @@ function renderStagingDownload(task) {
           onclick: () => {
             task.fileName = f;
             task.fileType = "";
-            for (let file of files.value)
+            for (const file of files.value)
               if (file._id === f) task.fileType = file["metadata.fileType"];
           }
         },
@@ -110,8 +110,8 @@ function renderStagingDownload(task) {
 }
 
 function renderStaging(staging) {
-  let elements = [];
-  for (let s of staging) {
+  const elements = [];
+  for (const s of staging) {
     const queueFunc = () => {
       staging.delete(s);
       taskQueue.queueTask(s);
@@ -143,19 +143,19 @@ function renderStaging(staging) {
 }
 
 function renderQueue(queue) {
-  let details = [];
-  let devices = {};
-  for (let t of queue) {
+  const details = [];
+  const devices = {};
+  for (const t of queue) {
     devices[t.device] = devices[t.device] || [];
     devices[t.device].push(t);
   }
 
-  for (let [k, v] of Object.entries(devices)) {
+  for (const [k, v] of Object.entries(devices)) {
     details.push(m("strong", k));
-    for (let t of v) {
-      let actions = [];
+    for (const t of v) {
+      const actions = [];
 
-      if (t.status === "fault" || t.status === "stale")
+      if (t.status === "fault" || t.status === "stale") {
         actions.push(
           m(
             "button",
@@ -168,6 +168,7 @@ function renderQueue(queue) {
             "↺"
           )
         );
+      }
 
       actions.push(
         m(
@@ -182,7 +183,7 @@ function renderQueue(queue) {
         )
       );
 
-      if (t.name === "setParameterValues")
+      if (t.name === "setParameterValues") {
         details.push(
           m(
             `div.${t.status}`,
@@ -197,7 +198,7 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else if (t.name === "refreshObject")
+      } else if (t.name === "refreshObject") {
         details.push(
           m(
             `div.${t.status}`,
@@ -205,13 +206,13 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else if (t.name === "reboot")
+      } else if (t.name === "reboot") {
         details.push(m(`div.${t.status}`, "Reboot", m(".actions", actions)));
-      else if (t.name === "factoryReset")
+      } else if (t.name === "factoryReset") {
         details.push(
           m(`div.${t.status}`, "Factory reset", m(".actions", actions))
         );
-      else if (t.name === "addObject")
+      } else if (t.name === "addObject") {
         details.push(
           m(
             `div.${t.status}`,
@@ -219,7 +220,7 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else if (t.name === "deleteObject")
+      } else if (t.name === "deleteObject") {
         details.push(
           m(
             `div.${t.status}`,
@@ -227,7 +228,7 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else if (t.name === "getParameterValues")
+      } else if (t.name === "getParameterValues") {
         details.push(
           m(
             `div.${t.status}`,
@@ -235,7 +236,7 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else if (t.name === "download")
+      } else if (t.name === "download") {
         details.push(
           m(
             `div.${t.status}`,
@@ -243,7 +244,9 @@ function renderQueue(queue) {
             m(".actions", actions)
           )
         );
-      else details.push(m(`div.${t.status}`, t.name, m(".actions", actions)));
+      } else {
+        details.push(m(`div.${t.status}`, t.name, m(".actions", actions)));
+      }
     }
   }
 
@@ -253,7 +256,7 @@ function renderQueue(queue) {
 function renderNotifications(notifs) {
   const notificationElements = [];
 
-  for (let n of notifs)
+  for (const n of notifs) {
     notificationElements.push(
       m(
         "div.notification",
@@ -276,6 +279,7 @@ function renderNotifications(notifs) {
         n.message
       )
     );
+  }
   return notificationElements;
 }
 
@@ -286,13 +290,13 @@ const component = {
     const notifs = notifications.getNotifications();
 
     let drawerElement, statusElement;
-    let notificationElements = renderNotifications(notifs);
-    let stagingElements = renderStaging(staging);
-    let queueElements = renderQueue(queue);
+    const notificationElements = renderNotifications(notifs);
+    const stagingElements = renderStaging(staging);
+    const queueElements = renderQueue(queue);
 
     function repositionNotifications() {
       let top = 10;
-      for (let c of notificationElements) {
+      for (const c of notificationElements) {
         c.dom.style.top = top;
         top += c.dom.offsetHeight + 10;
       }
@@ -300,20 +304,21 @@ const component = {
 
     function resizeDrawer() {
       let height = statusElement.dom.offsetTop + statusElement.dom.offsetHeight;
-      if (stagingElements.length)
-        for (let s of stagingElements)
+      if (stagingElements.length) {
+        for (const s of stagingElements)
           height = Math.max(height, s.dom.offsetTop + s.dom.offsetHeight);
-      else if (vnode.state.mouseIn)
-        for (let c of drawerElement.children)
+      } else if (vnode.state.mouseIn) {
+        for (const c of drawerElement.children)
           height = Math.max(height, c.dom.offsetTop + c.dom.offsetHeight);
+      }
       drawerElement.dom.style.height = height;
     }
 
     if (stagingElements.length + queueElements.length) {
       const statusCount = { queued: 0, pending: 0, fault: 0, stale: 0 };
-      for (let t of queue) statusCount[t.status] += 1;
+      for (const t of queue) statusCount[t.status] += 1;
 
-      let actions = m(
+      const actions = m(
         ".actions",
         m(
           "button.primary",
@@ -321,18 +326,20 @@ const component = {
             title: "Commit queued tasks",
             disabled: !statusCount.queued,
             onclick: () => {
-              let tasks = Array.from(taskQueue.getQueue()).filter(
+              const tasks = Array.from(taskQueue.getQueue()).filter(
                 t => t.status === "queued"
               );
               taskQueue
                 .commit(
                   tasks,
                   (deviceId, err, connectionRequestStatus, tasks2) => {
-                    if (err)
-                      return notifications.push(
+                    if (err) {
+                      notifications.push(
                         "error",
                         `${deviceId}: ${err.message}`
                       );
+                      return;
+                    }
 
                     if (connectionRequestStatus !== "OK") {
                       notifications.push(
@@ -342,7 +349,7 @@ const component = {
                       return;
                     }
 
-                    for (let t of tasks2)
+                    for (const t of tasks2) {
                       if (t.status === "stale") {
                         notifications.push(
                           "error",
@@ -356,6 +363,7 @@ const component = {
                         );
                         return;
                       }
+                    }
 
                     notifications.push(
                       "success",
diff --git a/client/faults-page.js b/client/faults-page.js
index 99b7388..47b48d7 100644
--- a/client/faults-page.js
+++ b/client/faults-page.js
@@ -24,10 +24,11 @@ const attributes = [
 ];
 
 const getDownloadUrl = memoize(filter => {
-  let cols = {};
-  for (let attr of attributes)
+  const cols = {};
+  for (const attr of attributes) {
     cols[attr.label] =
       attr.id === "timestamp" ? `DATE_STRING(${attr.id})` : attr.id;
+  }
 
   return `/api/faults.csv?${m.buildQueryString({
     filter: filter,
@@ -44,10 +45,11 @@ const unpackSmartQuery = memoize(query => {
 });
 
 function init(args) {
-  if (!window.authorizer.hasAccess("faults", 2))
+  if (!window.authorizer.hasAccess("faults", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   const sort = args.sort;
   const filter = args.filter;
@@ -68,16 +70,17 @@ function renderTable(
     type: "checkbox",
     checked: faults.length && selected.size === faults.length,
     onchange: e => {
-      for (let f of faults)
+      for (const f of faults) {
         if (e.target.checked) selected.add(f["_id"]);
         else selected.delete(f["_id"]);
+      }
     },
     disabled: !total
   });
 
   const labels = [m("th", selectAll)];
-  for (let attr of attributes) {
-    let label = attr.label;
+  for (const attr of attributes) {
+    const label = attr.label;
 
     let direction = 1;
 
@@ -85,7 +88,7 @@ function renderTable(
     if (sort[attr.id] > 0) symbol = "\u2bc6";
     else if (sort[attr.id] < 0) symbol = "\u2bc5";
 
-    let sortable = m(
+    const sortable = m(
       "button",
       {
         onclick: () => {
@@ -99,9 +102,9 @@ function renderTable(
     labels.push(m("th", [label, sortable]));
   }
 
-  let rows = [];
-  for (let f of faults) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const f of faults) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(f["_id"]),
       onchange: e => {
@@ -116,13 +119,14 @@ function renderTable(
 
     const deviceHref = `#!/devices/${encodeURIComponent(f["device"])}`;
 
-    let tds = [m("td", checkbox)];
-    for (let attr of attributes)
+    const tds = [m("td", checkbox)];
+    for (const attr of attributes) {
       if (attr.id === "device")
         tds.push(m("a", { href: deviceHref }, f[attr.id]));
       else if (attr.id === "timestamp")
         tds.push(m("td", new Date(f[attr.id]).toLocaleString()));
       else tds.push(m("td", f[attr.id]));
+    }
 
     rows.push(
       m(
@@ -145,7 +149,7 @@ function renderTable(
   if (!rows.length)
     rows.push(m("tr.empty", m("td", { colspan: 7 }, "No faults")));
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null) footerElements.push(`${faults.length}/${total}`);
   else footerElements.push(`${faults.length}`);
 
@@ -161,12 +165,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -217,13 +222,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/faults", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/faults", ops);
     }
@@ -232,16 +237,17 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let faults = store.fetch("faults", filter, {
+    const faults = store.fetch("faults", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
-    let count = store.count("faults", filter);
+    const count = store.count("faults", filter);
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let f of faults.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const f of faults.value)
         if (vnode.state.selected.has(f["_id"])) selected.add(f["_id"]);
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(vnode.attrs.filter);
diff --git a/client/files-page.js b/client/files-page.js
index 1dec116..6173f11 100644
--- a/client/files-page.js
+++ b/client/files-page.js
@@ -37,7 +37,7 @@ const attributes = [
   { id: "metadata.version", label: "Version" }
 ];
 
-let formData = {
+const formData = {
   resource: "files",
   attributes: attributes
     .slice(1) // remove _id from new object form
@@ -55,21 +55,21 @@ const unpackSmartQuery = memoize(query => {
 function putActionHandler(action, object) {
   return new Promise((resolve, reject) => {
     if (action === "save") {
-      let file = object["file"] ? object["file"][0] : null;
+      const file = object["file"] ? object["file"][0] : null;
       delete object["file"];
 
-      if (!file) return reject(new Error("File not selected"));
+      if (!file) return void reject(new Error("File not selected"));
 
-      let id = file.name;
+      const id = file.name;
 
       store
         .resourceExists("files", id)
         .then(exists => {
           if (exists) {
             store.fulfill(0, Date.now());
-            return reject(new Error("File already exists"));
+            return void reject(new Error("File already exists"));
           }
-          let headers = Object.assign(
+          const headers = Object.assign(
             {
               "Content-Type": "application/octet-stream",
               Accept: "application/octet-stream"
@@ -81,9 +81,7 @@ function putActionHandler(action, object) {
             method: "PUT",
             headers: headers,
             url: `/api/files/${encodeURIComponent(id)}`,
-            serialize: body => {
-              return body; // Identity function to prevent JSON.parse on blob data
-            },
+            serialize: body => body, // Identity function to prevent JSON.parse on blob data
             data: file
           })
             .then(() => {
@@ -104,8 +102,8 @@ function putActionHandler(action, object) {
 }
 
 const getDownloadUrl = memoize(filter => {
-  let cols = {};
-  for (let attr of attributes) cols[attr.label] = attr.id;
+  const cols = {};
+  for (const attr of attributes) cols[attr.label] = attr.id;
   return `/api/files.csv?${m.buildQueryString({
     filter: filter,
     columns: JSON.stringify(cols)
@@ -113,10 +111,11 @@ const getDownloadUrl = memoize(filter => {
 });
 
 function init(args) {
-  if (!window.authorizer.hasAccess("files", 2))
+  if (!window.authorizer.hasAccess("files", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   const sort = args.sort;
   const filter = args.filter;
@@ -137,16 +136,17 @@ function renderTable(
     type: "checkbox",
     checked: files.length && selected.size === files.length,
     onchange: e => {
-      for (let file of files)
+      for (const file of files) {
         if (e.target.checked) selected.add(file["_id"]);
         else selected.delete(file["_id"]);
+      }
     },
     disabled: !total
   });
 
   const labels = [m("th", selectAll)];
-  for (let attr of attributes) {
-    let label = attr.label;
+  for (const attr of attributes) {
+    const label = attr.label;
 
     let direction = 1;
 
@@ -154,7 +154,7 @@ function renderTable(
     if (sort[attr.id] > 0) symbol = "\u2bc6";
     else if (sort[attr.id] < 0) symbol = "\u2bc5";
 
-    let sortable = m(
+    const sortable = m(
       "button",
       {
         onclick: () => {
@@ -168,9 +168,9 @@ function renderTable(
     labels.push(m("th", [label, sortable]));
   }
 
-  let rows = [];
-  for (let file of files) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const file of files) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(file["_id"]),
       onchange: e => {
@@ -183,11 +183,12 @@ function renderTable(
       }
     });
 
-    let tds = [m("td", checkbox)];
-    for (let attr of attributes)
+    const tds = [m("td", checkbox)];
+    for (const attr of attributes) {
       if (attr.id == "script")
         tds.push(m("td", { title: file[attr.id] }, file[attr.id]));
       else tds.push(m("td", file[attr.id]));
+    }
 
     rows.push(
       m(
@@ -210,7 +211,7 @@ function renderTable(
   if (!rows.length)
     rows.push(m("tr.empty", m("td", { colspan: labels.length }, "No files")));
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null) footerElements.push(`${files.length}/${total}`);
   else footerElements.push(`${files.length}`);
 
@@ -226,12 +227,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -261,14 +263,14 @@ function renderTable(
     )
   ];
 
-  if (window.authorizer.hasAccess("files", 3))
+  if (window.authorizer.hasAccess("files", 3)) {
     buttons.push(
       m(
         "button.primary",
         {
           title: "Create new file",
           onclick: () => {
-            let cb = () => {
+            const cb = () => {
               return m(
                 putForm,
                 Object.assign(
@@ -295,6 +297,7 @@ function renderTable(
         "New"
       )
     );
+  }
 
   return [
     m(
@@ -317,13 +320,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/files", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/files", ops);
     }
@@ -332,17 +335,18 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let files = store.fetch("files", filter, {
+    const files = store.fetch("files", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
 
-    let count = store.count("files", filter);
+    const count = store.count("files", filter);
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let file of files.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const file of files.value)
         if (vnode.state.selected.has(file["_id"])) selected.add(file["_id"]);
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(vnode.attrs.filter);
diff --git a/client/filter-component.js b/client/filter-component.js
index 91b2249..32b102d 100644
--- a/client/filter-component.js
+++ b/client/filter-component.js
@@ -17,8 +17,8 @@ const getAutocomplete = memoize(resource => {
 
 function parseFilter(f) {
   if (/^[\s0-9a-zA-Z]+:/.test(f)) {
-    let k = f.split(":", 1)[0];
-    let v = f.slice(k.length + 1).trim();
+    const k = f.split(":", 1)[0];
+    const v = f.slice(k.length + 1).trim();
     return ["FUNC", "Q", k.trim(), v];
   }
   return expression.parse(f);
@@ -35,7 +35,7 @@ const splitFilter = memoize(filter => {
   const list = [];
   const f = expression.parse(filter);
   if (Array.isArray(f) && f[0] === "AND")
-    for (let ff of f.slice(1)) list.push(stringifyFilter(ff));
+    for (const ff of f.slice(1)) list.push(stringifyFilter(ff));
   else list.push(stringifyFilter(f));
 
   list.push("");
@@ -59,6 +59,7 @@ const component = {
         } catch (err) {
           vnode.state.filterInvalid |= 1 << idx;
         }
+        return null;
       });
       vnode.state.filterList.push("");
 
diff --git a/client/menu.js b/client/menu.js
index cf7ef8a..605d470 100644
--- a/client/menu.js
+++ b/client/menu.js
@@ -6,8 +6,8 @@ const menu = {
   view: vnode => {
     const active = { [vnode.attrs.page]: "active" };
 
-    let tabs = [];
-    if (window.authorizer.hasAccess("devices", 1))
+    const tabs = [];
+    if (window.authorizer.hasAccess("devices", 1)) {
       tabs.push(
         m(
           "li",
@@ -15,8 +15,9 @@ const menu = {
           m("a", { href: "#!/overview" }, "Overview")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("devices", 2))
+    if (window.authorizer.hasAccess("devices", 2)) {
       tabs.push(
         m(
           "li",
@@ -24,8 +25,9 @@ const menu = {
           m("a", { href: "#!/devices" }, "Devices")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("faults", 2))
+    if (window.authorizer.hasAccess("faults", 2)) {
       tabs.push(
         m(
           "li",
@@ -33,8 +35,9 @@ const menu = {
           m("a", { href: "#!/faults" }, "Faults")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("presets", 2))
+    if (window.authorizer.hasAccess("presets", 2)) {
       tabs.push(
         m(
           "li",
@@ -42,8 +45,9 @@ const menu = {
           m("a", { href: "#!/presets" }, "Presets")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("provisions", 2))
+    if (window.authorizer.hasAccess("provisions", 2)) {
       tabs.push(
         m(
           "li",
@@ -51,8 +55,9 @@ const menu = {
           m("a", { href: "#!/provisions" }, "Provisions")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("virtualParameters", 2))
+    if (window.authorizer.hasAccess("virtualParameters", 2)) {
       tabs.push(
         m(
           "li",
@@ -60,8 +65,9 @@ const menu = {
           m("a", { href: "#!/virtualParameters" }, "Virtual Parameters")
         )
       );
+    }
 
-    if (window.authorizer.hasAccess("files", 2))
+    if (window.authorizer.hasAccess("files", 2)) {
       tabs.push(
         m(
           "li",
@@ -69,6 +75,7 @@ const menu = {
           m("a", { href: "#!/files" }, "Files")
         )
       );
+    }
 
     return m("nav", m("ul", tabs));
   }
diff --git a/client/overlay.js b/client/overlay.js
index bca3be3..59f0331 100644
--- a/client/overlay.js
+++ b/client/overlay.js
@@ -18,7 +18,7 @@ function close(callback) {
 }
 
 function render() {
-  if (overlayCallback)
+  if (overlayCallback) {
     return m(
       ".overlay-wrapper",
       {
@@ -50,6 +50,7 @@ function render() {
         overlayCallback()
       )
     );
+  }
 
   return null;
 }
diff --git a/client/overview-page.js b/client/overview-page.js
index b0c4b29..cd81f5a 100644
--- a/client/overview-page.js
+++ b/client/overview-page.js
@@ -11,9 +11,10 @@ const memoizedParse = memoize(expression.parse);
 
 const GROUPS = config.ui.overview.groups;
 const CHARTS = {};
-for (let group of Object.values(GROUPS))
-  for (let chartName of Object.values(group["charts"]))
+for (const group of Object.values(GROUPS)) {
+  for (const chartName of Object.values(group["charts"]))
     CHARTS[chartName] = config.ui.overview.charts[chartName];
+}
 
 function queryCharts(charts) {
   charts = Object.assign({}, charts);
@@ -30,10 +31,11 @@ function queryCharts(charts) {
 }
 
 const init = function() {
-  if (!window.authorizer.hasAccess("devices", 1))
+  if (!window.authorizer.hasAccess("devices", 1)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   return Promise.resolve({ charts: queryCharts(CHARTS) });
 };
@@ -41,14 +43,14 @@ const init = function() {
 const component = {
   view: vnode => {
     document.title = "Overview - GenieACS";
-    let children = [];
-    for (let group of Object.values(GROUPS)) {
+    const children = [];
+    for (const group of Object.values(GROUPS)) {
       if (group.label) children.push(m("h1", group.label));
 
-      let groupChildren = [];
-      for (let chartName of Object.values(group.charts)) {
+      const groupChildren = [];
+      for (const chartName of Object.values(group.charts)) {
         const chart = vnode.attrs.charts[chartName];
-        let chartChildren = [];
+        const chartChildren = [];
         if (chart.label) chartChildren.push(m("h2", chart.label));
 
         chartChildren.push(m(pieChartComponent, { chart: chart }));
diff --git a/client/pie-chart-component.js b/client/pie-chart-component.js
index add0044..71a79a4 100644
--- a/client/pie-chart-component.js
+++ b/client/pie-chart-component.js
@@ -3,21 +3,21 @@
 import m from "mithril";
 
 const drawChart = function(chartData) {
-  let slices = chartData.slices;
-  let total = Array.from(Object.values(chartData.slices)).reduce(
+  const slices = chartData.slices;
+  const total = Array.from(Object.values(chartData.slices)).reduce(
     (a, s) => a + (s.count.value || 0),
     0
   );
-  let legend = [];
-  let paths = [];
-  let links = [];
+  const legend = [];
+  const paths = [];
+  const links = [];
   let currentProgressPercentage = 0;
   let startX = Math.cos(2 * Math.PI * currentProgressPercentage) * 100;
   let startY = Math.sin(2 * Math.PI * currentProgressPercentage) * 100;
   let endX, endY;
 
-  for (let slice of Object.values(slices)) {
-    let percent = total > 0 ? (slice.count.value || 0) / total : 0;
+  for (const slice of Object.values(slices)) {
+    const percent = total > 0 ? (slice.count.value || 0) / total : 0;
     legend.push(
       m(".legend-line", [
         m("span.color", {
@@ -41,9 +41,9 @@ const drawChart = function(chartData) {
       currentProgressPercentage += percent;
       endX = Math.cos(2 * Math.PI * currentProgressPercentage) * 100;
       endY = Math.sin(2 * Math.PI * currentProgressPercentage) * 100;
-      let isBigArc = percent > 0.5 ? 1 : 0;
+      const isBigArc = percent > 0.5 ? 1 : 0;
 
-      let sketch =
+      const sketch =
         `M ${startX} ${startY} ` + // Move to the starting point
         `A 100 100 0 ${isBigArc} 1 ${endX} ${endY} ` + // Draw an Arc from starting point to ending point
         `L 0 0 z`; // complete the shape by drawing a line to the center of circle
@@ -58,9 +58,9 @@ const drawChart = function(chartData) {
         })
       );
 
-      let percentageX =
+      const percentageX =
         Math.cos(2 * Math.PI * (currentProgressPercentage - percent / 2)) * 50;
-      let percentageY =
+      const percentageY =
         Math.sin(2 * Math.PI * (currentProgressPercentage - percent / 2)) * 50;
 
       links.push(
diff --git a/client/presets-page.js b/client/presets-page.js
index f51a842..3c1dff0 100644
--- a/client/presets-page.js
+++ b/client/presets-page.js
@@ -39,10 +39,10 @@ const unpackSmartQuery = memoize(query => {
 
 function putActionHandler(action, object, isNew) {
   if (action === "save") {
-    let id = object["_id"];
+    const id = object["_id"];
     delete object["_id"];
 
-    if (!id) return notifications.push("error", "ID can not be empty");
+    if (!id) return void notifications.push("error", "ID can not be empty");
 
     store
       .resourceExists("presets", id)
@@ -90,14 +90,14 @@ function putActionHandler(action, object, isNew) {
   }
 }
 
-let formData = {
+const formData = {
   resource: "presets",
   attributes: attributes
 };
 
 const getDownloadUrl = memoize(filter => {
-  let cols = {};
-  for (let attr of attributes) cols[attr.label] = attr.id;
+  const cols = {};
+  for (const attr of attributes) cols[attr.label] = attr.id;
   return `/api/presets.csv?${m.buildQueryString({
     filter: filter,
     columns: JSON.stringify(cols)
@@ -105,10 +105,11 @@ const getDownloadUrl = memoize(filter => {
 });
 
 function init(args) {
-  if (!window.authorizer.hasAccess("presets", 2))
+  if (!window.authorizer.hasAccess("presets", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   const sort = args.sort;
   const filter = args.filter;
@@ -129,17 +130,18 @@ function renderTable(
     type: "checkbox",
     checked: presets.length && selected.size === presets.length,
     onchange: e => {
-      for (let preset of presets)
+      for (const preset of presets) {
         if (e.target.checked) selected.add(preset["_id"]);
         else selected.delete(preset["_id"]);
+      }
     },
     disabled: !total
   });
 
   const labels = [m("th", selectAll)];
 
-  for (let attr of attributes) {
-    let label = attr.label;
+  for (const attr of attributes) {
+    const label = attr.label;
 
     if (attr.unsortable) {
       labels.push(m("th", label));
@@ -152,7 +154,7 @@ function renderTable(
     if (sort[attr.id] > 0) symbol = "\u2bc6";
     else if (sort[attr.id] < 0) symbol = "\u2bc5";
 
-    let sortable = m(
+    const sortable = m(
       "button",
       {
         onclick: () => {
@@ -166,9 +168,9 @@ function renderTable(
     labels.push(m("th", [label, sortable]));
   }
 
-  let rows = [];
-  for (let preset of presets) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const preset of presets) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(preset["_id"]),
       onchange: e => {
@@ -182,14 +184,15 @@ function renderTable(
     });
 
     let devicesUrl = "/#!/devices";
-    if (preset["precondition"].length)
+    if (preset["precondition"].length) {
       devicesUrl += `?${m.buildQueryString({
         filter: preset["precondition"]
       })}`;
+    }
 
-    let tds = [m("td", checkbox)];
-    for (let attr of attributes)
-      if (attr.id === "precondition")
+    const tds = [m("td", checkbox)];
+    for (const attr of attributes) {
+      if (attr.id === "precondition") {
         tds.push(
           m(
             "td",
@@ -197,7 +200,10 @@ function renderTable(
             m("a", { href: devicesUrl }, preset[attr.id])
           )
         );
-      else tds.push(m("td", preset[attr.id]));
+      } else {
+        tds.push(m("td", preset[attr.id]));
+      }
+    }
 
     tds.push(
       m(
@@ -206,7 +212,7 @@ function renderTable(
           "a",
           {
             onclick: () => {
-              let cb = () => {
+              const cb = () => {
                 return m(
                   putForm,
                   Object.assign(
@@ -250,7 +256,7 @@ function renderTable(
   if (!rows.length)
     rows.push(m("tr.empty", m("td", { colspan: labels.length }, "No presets")));
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null) footerElements.push(`${presets.length}/${total}`);
   else footerElements.push(`${presets.length}`);
 
@@ -266,12 +272,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -301,14 +308,14 @@ function renderTable(
     )
   ];
 
-  if (window.authorizer.hasAccess("presets", 3))
+  if (window.authorizer.hasAccess("presets", 3)) {
     buttons.push(
       m(
         "button.primary",
         {
           title: "Create new preset",
           onclick: () => {
-            let cb = () => {
+            const cb = () => {
               return m(
                 putForm,
                 Object.assign(
@@ -328,6 +335,7 @@ function renderTable(
         "New"
       )
     );
+  }
 
   return [
     m(
@@ -350,13 +358,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/presets", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/presets", ops);
     }
@@ -365,15 +373,15 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let presets = store.fetch("presets", filter, {
+    const presets = store.fetch("presets", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
-    let count = store.count("presets", filter);
+    const count = store.count("presets", filter);
 
     const provisions = store.fetch("provisions", true);
     if (provisions.fulfilled) {
-      let provisionAttr = attributes.find(attr => {
+      const provisionAttr = attributes.find(attr => {
         return attr.id === "provision";
       });
       provisionAttr.options = provisions.value.map(v => {
@@ -381,11 +389,13 @@ const component = {
       });
     }
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let preset of presets.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const preset of presets.value) {
         if (vnode.state.selected.has(preset["_id"]))
           selected.add(preset["_id"]);
+      }
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(vnode.attrs.filter);
diff --git a/client/provisions-page.js b/client/provisions-page.js
index 52d1c66..0f61c5c 100644
--- a/client/provisions-page.js
+++ b/client/provisions-page.js
@@ -34,10 +34,10 @@ const unpackSmartQuery = memoize(query => {
 
 function putActionHandler(action, object, isNew) {
   if (action === "save") {
-    let id = object["_id"];
+    const id = object["_id"];
     delete object["_id"];
 
-    if (!id) return notifications.push("error", "ID can not be empty");
+    if (!id) return void notifications.push("error", "ID can not be empty");
 
     store
       .resourceExists("provisions", id)
@@ -85,14 +85,14 @@ function putActionHandler(action, object, isNew) {
   }
 }
 
-let formData = {
+const formData = {
   resource: "provisions",
   attributes: attributes
 };
 
 const getDownloadUrl = memoize(filter => {
-  let cols = {};
-  for (let attr of attributes) cols[attr.label] = attr.id;
+  const cols = {};
+  for (const attr of attributes) cols[attr.label] = attr.id;
   return `/api/provisions.csv?${m.buildQueryString({
     filter: filter,
     columns: JSON.stringify(cols)
@@ -100,10 +100,11 @@ const getDownloadUrl = memoize(filter => {
 });
 
 function init(args) {
-  if (!window.authorizer.hasAccess("provisions", 2))
+  if (!window.authorizer.hasAccess("provisions", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   const sort = args.sort;
   const filter = args.filter;
@@ -131,16 +132,17 @@ function renderTable(
     type: "checkbox",
     checked: provisions.length && selected.size === provisions.length,
     onchange: e => {
-      for (let provision of provisions)
+      for (const provision of provisions) {
         if (e.target.checked) selected.add(provision["_id"]);
         else selected.delete(provision["_id"]);
+      }
     },
     disabled: !total
   });
 
   const labels = [m("th", selectAll)];
-  for (let attr of attributes) {
-    let label = attr.label;
+  for (const attr of attributes) {
+    const label = attr.label;
 
     let direction = 1;
 
@@ -148,7 +150,7 @@ function renderTable(
     if (sort[attr.id] > 0) symbol = "\u2bc6";
     else if (sort[attr.id] < 0) symbol = "\u2bc5";
 
-    let sortable = m(
+    const sortable = m(
       "button",
       {
         onclick: () => {
@@ -162,9 +164,9 @@ function renderTable(
     labels.push(m("th", [label, sortable]));
   }
 
-  let rows = [];
-  for (let provision of provisions) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const provision of provisions) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(provision["_id"]),
       onchange: e => {
@@ -177,11 +179,12 @@ function renderTable(
       }
     });
 
-    let tds = [m("td", checkbox)];
-    for (let attr of attributes)
+    const tds = [m("td", checkbox)];
+    for (const attr of attributes) {
       if (attr.id == "script")
         tds.push(m("td", { title: provision[attr.id] }, provision[attr.id]));
       else tds.push(m("td", provision[attr.id]));
+    }
 
     tds.push(
       m(
@@ -190,7 +193,7 @@ function renderTable(
           "a",
           {
             onclick: () => {
-              let cb = () => {
+              const cb = () => {
                 return m(
                   putForm,
                   Object.assign(
@@ -232,12 +235,13 @@ function renderTable(
     );
   }
 
-  if (!rows.length)
+  if (!rows.length) {
     rows.push(
       m("tr.empty", m("td", { colspan: labels.length }, "No provisions"))
     );
+  }
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null) footerElements.push(`${provisions.length}/${total}`);
   else footerElements.push(`${provisions.length}`);
 
@@ -253,12 +257,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -290,14 +295,14 @@ function renderTable(
     )
   ];
 
-  if (window.authorizer.hasAccess("provisions", 3))
+  if (window.authorizer.hasAccess("provisions", 3)) {
     buttons.push(
       m(
         "button.primary",
         {
           title: "Create new provision",
           onclick: () => {
-            let cb = () => {
+            const cb = () => {
               return m(
                 putForm,
                 Object.assign(
@@ -317,6 +322,7 @@ function renderTable(
         "New"
       )
     );
+  }
 
   return [
     m(
@@ -339,13 +345,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/provisions", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/provisions", ops);
     }
@@ -354,18 +360,20 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let provisions = store.fetch("provisions", filter, {
+    const provisions = store.fetch("provisions", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
 
-    let count = store.count("provisions", filter);
+    const count = store.count("provisions", filter);
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let provision of provisions.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const provision of provisions.value) {
         if (vnode.state.selected.has(provision["_id"]))
           selected.add(provision["_id"]);
+      }
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(vnode.attrs.filter);
diff --git a/client/smart-query.js b/client/smart-query.js
index 256e6ed..50155f1 100644
--- a/client/smart-query.js
+++ b/client/smart-query.js
@@ -3,7 +3,7 @@
 import config from "./config";
 import * as expression from "../common/expression";
 
-let resources = {
+const resources = {
   devices: {},
   faults: {
     Device: { parameter: ["PARAM", "device"], type: "string" },
@@ -35,11 +35,12 @@ let resources = {
   }
 };
 
-for (let v of Object.values(config.ui.filters))
+for (const v of Object.values(config.ui.filters)) {
   resources.devices[v.label] = {
     parameter: expression.parse(v.parameter),
     type: (v.type || "").split(",").map(s => s.trim())
   };
+}
 
 function getLabels(resource) {
   if (!resources[resource]) return [];
@@ -48,14 +49,15 @@ function getLabels(resource) {
 
 function queryNumber(param, value) {
   let op = "=";
-  for (let o of ["<>", "=", "<=", "<", ">=", ">"])
+  for (const o of ["<>", "=", "<=", "<", ">=", ">"]) {
     if (value.startsWith(o)) {
       op = o;
       value = value.slice(o.length).trim();
       break;
     }
+  }
 
-  let v = parseInt(value);
+  const v = parseInt(value);
   if (v !== +value) return null;
 
   return [op, param, v];
@@ -68,12 +70,13 @@ function queryString(param, value) {
 function queryMac(param, value) {
   value = value.replace(/[^a-f0-9]/gi, "").toLowerCase();
   if (!value) return null;
-  if (value.length === 12)
+  if (value.length === 12) {
     return [
       "LIKE",
       ["FUNC", "LOWER", param],
       value.replace(/(..)(?!$)/g, "$1:")
     ];
+  }
 
   return [
     "OR",
@@ -90,20 +93,20 @@ function unpack(resource, label, value) {
   if (!resources[resource]) return null;
   const type = resources[resource][label].type;
   value = value.trim();
-  let res = ["OR"];
+  const res = ["OR"];
 
   if (type.length === 0 || type.includes("number")) {
-    let q = queryNumber(resources[resource][label].parameter, value);
+    const q = queryNumber(resources[resource][label].parameter, value);
     if (q) res.push(q);
   }
 
   if (type.length === 0 || type.includes("string")) {
-    let q = queryString(resources[resource][label].parameter, value);
+    const q = queryString(resources[resource][label].parameter, value);
     if (q) res.push(q);
   }
 
   if (type.includes("mac")) {
-    let q = queryMac(resources[resource][label].parameter, value);
+    const q = queryMac(resources[resource][label].parameter, value);
     if (q) res.push(q);
   }
 
diff --git a/client/store.js b/client/store.js
index dab64a2..f2d5bf5 100644
--- a/client/store.js
+++ b/client/store.js
@@ -1,7 +1,6 @@
 "use strict";
 
 import m from "mithril";
-import config from "./config";
 import * as expressionParser from "../common/expression-parser";
 import * as expression from "../common/expression";
 import memoize from "../common/memoize";
@@ -23,7 +22,7 @@ const queries = {
 };
 
 const resources = {};
-for (let r of [
+for (const r of [
   "devices",
   "faults",
   "files",
@@ -31,13 +30,14 @@ for (let r of [
   "provisions",
   "virtualParameters",
   "files"
-])
+]) {
   resources[r] = {
     objects: new Map(),
     count: new Map(),
     fetch: new Map(),
     combinedFilter: null
   };
+}
 
 class QueryResponse {
   get fulfilled() {
@@ -79,11 +79,12 @@ function limitFilter(filter, sort, bookmark) {
     arr.reduce((cur, kv) => {
       const [param, asc] = kv;
       if (asc <= 0) {
-        if (bookmark[param] == null)
+        if (bookmark[param] == null) {
           return expression.or(
             ["IS NOT NULL", ["PARAM", param]],
             expression.and(["IS NULL", ["PARAM", param]], cur)
           );
+        }
 
         let f = null;
 
@@ -124,13 +125,15 @@ function compareFunction(sort) {
     for (const [param, asc] of sortEntries) {
       let v1 = a[param];
       let v2 = b[param];
-      if (v1 != null && typeof v1 === "object")
+      if (v1 != null && typeof v1 === "object") {
         if (v1.value) v1 = v1.value[0];
         else v1 = null;
+      }
 
-      if (v2 != null && typeof v2 === "object")
+      if (v2 != null && typeof v2 === "object") {
         if (v2.value) v2 = v2.value[0];
         else v2 = null;
+      }
 
       if (v1 > v2) {
         return asc;
@@ -153,23 +156,24 @@ function compareFunction(sort) {
 
 function findMatches(resourceType, filter, sort, limit) {
   // Handle "tag =" and "tag <>" special cases
-  if (resourceType === "devices")
+  if (resourceType === "devices") {
     filter = expressionParser.map(filter, e => {
       if (
         Array.isArray(e) &&
         Array.isArray(e[1]) &&
         e[1][0] === "PARAM" &&
         e[1][1] === "tag"
-      )
+      ) {
         if (e[0] === "=") return ["IS NOT NULL", ["PARAM", `Tags.${e[2]}`]];
         else if (e[0] === "<>") return ["IS NULL", ["PARAM", `Tags.${e[2]}`]];
+      }
       return e;
     });
+  }
 
   let value = [];
-  for (let obj of resources[resourceType].objects.values())
-    if (expression.evaluate(filter, obj, fulfillTimestamp))
-      value.push(obj);
+  for (const obj of resources[resourceType].objects.values())
+    if (expression.evaluate(filter, obj, fulfillTimestamp)) value.push(obj);
 
   value = value.sort(compareFunction(sort));
   if (limit) value = value.slice(0, limit);
@@ -181,7 +185,7 @@ function inferQuery(resourceType, queryResponse) {
   const limit = queries.limit.get(queryResponse);
   let filter = queries.filter.get(queryResponse);
   filter = unpackExpression(filter);
-  let bookmark = queries.bookmark.get(queryResponse);
+  const bookmark = queries.bookmark.get(queryResponse);
   const sort = queries.sort.get(queryResponse);
   if (bookmark || !limit) {
     if (bookmark) filter = limitFilter(filter, sort, bookmark);
@@ -208,7 +212,7 @@ function fetch(resourceType, filter, options = {}) {
     sort["DeviceID.ID"] = sort["DeviceID.ID"] || 1;
   else sort["_id"] = sort["_id"] || 1;
 
-  let key = `${filterStr}:${limit}:${JSON.stringify(sort)}`;
+  const key = `${filterStr}:${limit}:${JSON.stringify(sort)}`;
   let queryResponse = resources[resourceType].fetch.get(key);
   if (queryResponse) return queryResponse;
 
@@ -225,15 +229,15 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
   let updated = false;
 
   if (_fulfillTimestamp > fulfillTimestamp) {
-    for (let resource of Object.values(resources))
+    for (const resource of Object.values(resources))
       resource.combinedFilter = null;
     fulfillTimestamp = _fulfillTimestamp;
   }
 
   const allPromises = [];
 
-  for (let [resourceType, resource] of Object.entries(resources))
-    for (let [queryResponseKey, queryResponse] of resource.count) {
+  for (const [resourceType, resource] of Object.entries(resources)) {
+    for (const [queryResponseKey, queryResponse] of resource.count) {
       if (!(queries.accessed.get(queryResponse) >= accessTimestamp)) {
         resource.count.delete(queryResponseKey);
         continue;
@@ -269,11 +273,12 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
         );
       }
     }
+  }
 
-  let toFetchAll = {};
+  const toFetchAll = {};
 
-  for (let [resourceType, resource] of Object.entries(resources))
-    for (let [queryResponseKey, queryResponse] of resource.fetch) {
+  for (const [resourceType, resource] of Object.entries(resources)) {
+    for (const [queryResponseKey, queryResponse] of resource.fetch) {
       if (!(queries.accessed.get(queryResponse) >= accessTimestamp)) {
         resource.fetch.delete(queryResponseKey);
         continue;
@@ -287,7 +292,7 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
         toFetchAll[resourceType].push(queryResponse);
         const limit = queries.limit.get(queryResponse);
         const sort = queries.sort.get(queryResponse);
-        if (limit)
+        if (limit) {
           allPromises.push(
             new Promise((resolve, reject) => {
               updated = true;
@@ -308,12 +313,15 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
                 .then(res => {
                   if (res.length) {
                     // Generate bookmark object
-                    let bm = Object.keys(sort).reduce((b, k) => {
-                      if (res[0][k] != null)
+                    const bm = Object.keys(sort).reduce((b, k) => {
+                      if (res[0][k] != null) {
                         if (typeof res[0][k] === "object") {
                           if (res[0][k].value != null)
                             b[k] = res[0][k].value[0];
-                        } else b[k] = res[0][k];
+                        } else {
+                          b[k] = res[0][k];
+                        }
+                      }
 
                       return b;
                     }, {});
@@ -326,8 +334,10 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
                 .catch(reject);
             })
           );
+        }
       }
     }
+  }
 
   return new Promise((resolve, reject) => {
     Promise.all(allPromises)
@@ -368,11 +378,12 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
           if (!resources[resourceType].combinedFilter)
             deleted = new Set(resources[resourceType].objects.keys());
           let combinedFilterDiff = combinedFilter;
-          if (resources[resourceType].combinedFilter)
+          if (resources[resourceType].combinedFilter) {
             combinedFilterDiff = expression.and(
               combinedFilterDiff,
               expression.not(resources[resourceType].combinedFilter)
             );
+          }
           resources[resourceType].combinedFilter = expression.or(
             combinedFilter,
             resources[resourceType].combinedFilter
@@ -389,7 +400,7 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
                   })
               })
                 .then(res => {
-                  for (let r of res) {
+                  for (const r of res) {
                     const id =
                       resourceType === "devices"
                         ? r["DeviceID.ID"].value[0]
@@ -398,7 +409,7 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
                     deleted.delete(id);
                   }
 
-                  for (let d of deleted) {
+                  for (const d of deleted) {
                     const obj = resources[resourceType].objects.get(d);
                     if (
                       expression.evaluate(
@@ -410,7 +421,7 @@ function fulfill(accessTimestamp, _fulfillTimestamp) {
                       resources[resourceType].objects.delete(d);
                   }
 
-                  for (let queryResponse of toFetch) {
+                  for (const queryResponse of toFetch) {
                     let filter = queries.filter.get(queryResponse);
                     filter = unpackExpression(filter);
                     const limit = queries.limit.get(queryResponse);
@@ -444,7 +455,7 @@ function getTimestamp() {
 }
 
 function postTasks(deviceId, tasks) {
-  for (let t of tasks) {
+  for (const t of tasks) {
     t.status = "pending";
     t.device = deviceId;
   }
@@ -459,8 +470,8 @@ function postTasks(deviceId, tasks) {
         const connectionRequestStatus = xhr.getResponseHeader(
           "Connection-Request"
         );
-        let st = JSON.parse(xhr.response);
-        for (let [i, t] of st.entries()) {
+        const st = JSON.parse(xhr.response);
+        for (const [i, t] of st.entries()) {
           tasks[i]._id = t._id;
           tasks[i].status = t.status;
           tasks[i].fault = t.fault;
@@ -487,7 +498,7 @@ function deleteResource(resourceType, id) {
 }
 
 function putResource(resourceType, id, object) {
-  for (let k in object) if (object[k] === undefined) object[k] = null;
+  for (const k in object) if (object[k] === undefined) object[k] = null;
 
   return m.request({
     method: "PUT",
@@ -498,7 +509,7 @@ function putResource(resourceType, id, object) {
 
 function resourceExists(resource, id) {
   const param = resource === "devices" ? "DeviceID.ID" : "_id";
-  let filter = ["=", ["PARAM", param], id];
+  const filter = ["=", ["PARAM", param], id];
   return m.request({
     method: "HEAD",
     url:
diff --git a/client/task-queue.js b/client/task-queue.js
index df0b9db..b24244d 100644
--- a/client/task-queue.js
+++ b/client/task-queue.js
@@ -41,8 +41,8 @@ function stageDownload(task) {
 }
 
 function commit(tasks, callback) {
-  let devices = {};
-  for (let t of tasks) {
+  const devices = {};
+  for (const t of tasks) {
     devices[t.device] = devices[t.device] || [];
     devices[t.device].push(t);
     queueTask(t);
@@ -50,19 +50,20 @@ function commit(tasks, callback) {
 
   return new Promise(resolve => {
     let counter = 1;
-    for (let [deviceId, tasks2] of Object.entries(devices)) {
+    for (const [deviceId, tasks2] of Object.entries(devices)) {
       ++counter;
       store
         .postTasks(deviceId, tasks)
         .then(connectionRequestStatus => {
-          for (let t of tasks2)
+          for (const t of tasks2) {
             if (t.status === "pending") t.status = "stale";
             else if (t.status === "done") queue.delete(t);
+          }
           callback(deviceId, null, connectionRequestStatus, tasks2);
           if (--counter === 0) resolve();
         })
         .catch(err => {
-          for (let t of tasks2) t.status = "stale";
+          for (const t of tasks2) t.status = "stale";
           callback(deviceId, err, null, tasks2);
           if (--counter === 0) resolve();
         });
diff --git a/client/timeago.js b/client/timeago.js
index b4f1d2c..c0143ab 100644
--- a/client/timeago.js
+++ b/client/timeago.js
@@ -13,7 +13,7 @@ function timeAgo(dtime) {
   let res = "";
   let level = 2;
 
-  for (const [u, t] of Object.entries(UNITS))
+  for (const [u, t] of Object.entries(UNITS)) {
     if (dtime >= t) {
       let n;
       if (level > 1) {
@@ -26,6 +26,7 @@ function timeAgo(dtime) {
       else res += `${n} ${u} `;
       if (!--level) break;
     }
+  }
 
   return res + "ago";
 }
diff --git a/client/user-menu.js b/client/user-menu.js
index 7eeff90..3a01528 100644
--- a/client/user-menu.js
+++ b/client/user-menu.js
@@ -7,7 +7,7 @@ import * as notifications from "./notifications";
 
 const userMenu = {
   view: () => {
-    if (window.username)
+    if (window.username) {
       return m(
         "div.user-menu",
         window.username,
@@ -32,7 +32,7 @@ const userMenu = {
           "Log out"
         )
       );
-    else
+    } else {
       return m(
         "div.user-menu",
         m(
@@ -43,6 +43,7 @@ const userMenu = {
           "Log in"
         )
       );
+    }
   }
 };
 
diff --git a/client/virtual-parameters-page.js b/client/virtual-parameters-page.js
index 2f62d07..1f32be5 100644
--- a/client/virtual-parameters-page.js
+++ b/client/virtual-parameters-page.js
@@ -34,10 +34,10 @@ const unpackSmartQuery = memoize(query => {
 
 function putActionHandler(action, object, isNew) {
   if (action === "save") {
-    let id = object["_id"];
+    const id = object["_id"];
     delete object["_id"];
 
-    if (!id) return notifications.push("error", "ID can not be empty");
+    if (!id) return void notifications.push("error", "ID can not be empty");
 
     store
       .resourceExists("virtualParameters", id)
@@ -85,14 +85,14 @@ function putActionHandler(action, object, isNew) {
   }
 }
 
-let formData = {
+const formData = {
   resource: "virtualParameters",
   attributes: attributes
 };
 
 const getDownloadUrl = memoize(filter => {
-  let cols = {};
-  for (let attr of attributes) cols[attr.label] = attr.id;
+  const cols = {};
+  for (const attr of attributes) cols[attr.label] = attr.id;
   return `/api/virtualParameters.csv?${m.buildQueryString({
     filter: filter,
     columns: JSON.stringify(cols)
@@ -100,10 +100,11 @@ const getDownloadUrl = memoize(filter => {
 });
 
 function init(args) {
-  if (!window.authorizer.hasAccess("virtualParameters", 2))
+  if (!window.authorizer.hasAccess("virtualParameters", 2)) {
     return Promise.reject(
       new Error("You are not authorized to view this page")
     );
+  }
 
   const sort = args.sort;
   const filter = args.filter;
@@ -132,16 +133,17 @@ function renderTable(
     checked:
       virtualParameters.length && selected.size === virtualParameters.length,
     onchange: e => {
-      for (let virtualParameter of virtualParameters)
+      for (const virtualParameter of virtualParameters) {
         if (e.target.checked) selected.add(virtualParameter["_id"]);
         else selected.delete(virtualParameter["_id"]);
+      }
     },
     disabled: !total
   });
 
   const labels = [m("th", selectAll)];
-  for (let attr of attributes) {
-    let label = attr.label;
+  for (const attr of attributes) {
+    const label = attr.label;
 
     let direction = 1;
 
@@ -149,7 +151,7 @@ function renderTable(
     if (sort[attr.id] > 0) symbol = "\u2bc6";
     else if (sort[attr.id] < 0) symbol = "\u2bc5";
 
-    let sortable = m(
+    const sortable = m(
       "button",
       {
         onclick: () => {
@@ -163,9 +165,9 @@ function renderTable(
     labels.push(m("th", [label, sortable]));
   }
 
-  let rows = [];
-  for (let virtualParameter of virtualParameters) {
-    let checkbox = m("input", {
+  const rows = [];
+  for (const virtualParameter of virtualParameters) {
+    const checkbox = m("input", {
       type: "checkbox",
       checked: selected.has(virtualParameter["_id"]),
       onchange: e => {
@@ -178,9 +180,9 @@ function renderTable(
       }
     });
 
-    let tds = [m("td", checkbox)];
-    for (let attr of attributes)
-      if (attr.id == "script")
+    const tds = [m("td", checkbox)];
+    for (const attr of attributes) {
+      if (attr.id == "script") {
         tds.push(
           m(
             "td",
@@ -188,7 +190,10 @@ function renderTable(
             virtualParameter[attr.id]
           )
         );
-      else tds.push(m("td", virtualParameter[attr.id]));
+      } else {
+        tds.push(m("td", virtualParameter[attr.id]));
+      }
+    }
 
     tds.push(
       m(
@@ -197,7 +202,7 @@ function renderTable(
           "a",
           {
             onclick: () => {
-              let cb = () => {
+              const cb = () => {
                 return m(
                   putForm,
                   Object.assign(
@@ -239,15 +244,16 @@ function renderTable(
     );
   }
 
-  if (!rows.length)
+  if (!rows.length) {
     rows.push(
       m(
         "tr.empty",
         m("td", { colspan: labels.length }, "No virtual parameters")
       )
     );
+  }
 
-  let footerElements = [];
+  const footerElements = [];
   if (total != null)
     footerElements.push(`${virtualParameters.length}/${total}`);
   else footerElements.push(`${virtualParameters.length}`);
@@ -266,12 +272,13 @@ function renderTable(
     )
   );
 
-  if (downloadUrl)
+  if (downloadUrl) {
     footerElements.push(
       m("a.download-csv", { href: downloadUrl, download: "" }, "Download")
     );
+  }
 
-  let tfoot = m(
+  const tfoot = m(
     "tfoot",
     m("tr", m("td", { colspan: labels.length }, footerElements))
   );
@@ -306,14 +313,14 @@ function renderTable(
     )
   ];
 
-  if (window.authorizer.hasAccess("virtualParameters", 3))
+  if (window.authorizer.hasAccess("virtualParameters", 3)) {
     buttons.push(
       m(
         "button.primary",
         {
           title: "Create new virtual parameter",
           onclick: () => {
-            let cb = () => {
+            const cb = () => {
               return m(
                 putForm,
                 Object.assign(
@@ -333,6 +340,7 @@ function renderTable(
         "New"
       )
     );
+  }
 
   return [
     m(
@@ -355,13 +363,13 @@ const component = {
     }
 
     function onFilterChanged(filter) {
-      let ops = { filter };
+      const ops = { filter };
       if (vnode.attrs.sort) ops.sort = vnode.attrs.sort;
       m.route.set("/virtualParameters", ops);
     }
 
     function onSortChange(sort) {
-      let ops = { sort };
+      const ops = { sort };
       if (vnode.attrs.filter) ops.filter = vnode.attrs.filter;
       m.route.set("/virtualParameters", ops);
     }
@@ -370,18 +378,20 @@ const component = {
     let filter = vnode.attrs.filter ? memoizedParse(vnode.attrs.filter) : true;
     filter = unpackSmartQuery(filter);
 
-    let virtualParameters = store.fetch("virtualParameters", filter, {
+    const virtualParameters = store.fetch("virtualParameters", filter, {
       limit: vnode.state.showCount || PAGE_SIZE,
       sort: sort
     });
 
-    let count = store.count("virtualParameters", filter);
+    const count = store.count("virtualParameters", filter);
 
-    let selected = new Set();
-    if (vnode.state.selected)
-      for (let virtualParameter of virtualParameters.value)
+    const selected = new Set();
+    if (vnode.state.selected) {
+      for (const virtualParameter of virtualParameters.value) {
         if (vnode.state.selected.has(virtualParameter["_id"]))
           selected.add(virtualParameter["_id"]);
+      }
+    }
     vnode.state.selected = selected;
 
     const downloadUrl = getDownloadUrl(vnode.attrs.filter);
diff --git a/common/authorizer.js b/common/authorizer.js
index 0288142..82bb3b1 100644
--- a/common/authorizer.js
+++ b/common/authorizer.js
@@ -1,7 +1,5 @@
 "use strict";
 
-const expression = require("./expression");
-
 const validators = {
   pass: require("./validators/pass"),
   test: require("./validators/test")
@@ -16,17 +14,18 @@ class Authorizer {
 
   hasAccess(resourceType, access) {
     const cacheKey = `${resourceType}-${access}`;
-    if (cacheKey in this.hasAccessCache)
-      return this.hasAccessCache[cacheKey];
+    if (cacheKey in this.hasAccessCache) return this.hasAccessCache[cacheKey];
 
     let has = false;
-    for (let permissionSet of this.permissionSets) {
-      for (let perm of permissionSet)
-        if (perm[resourceType])
+    for (const permissionSet of this.permissionSets) {
+      for (const perm of permissionSet) {
+        if (perm[resourceType]) {
           if (perm[resourceType].access >= access) {
             has = true;
             break;
           }
+        }
+      }
     }
 
     this.hasAccessCache[cacheKey] = has;
@@ -39,23 +38,26 @@ class Authorizer {
 
     let funcs = {};
 
-    for (let permissionSet of this.permissionSets)
-      for (let perm of permissionSet)
+    for (const permissionSet of this.permissionSets) {
+      for (const perm of permissionSet) {
         if (perm[resourceType]) {
           if (perm[resourceType].access >= 3) {
-            if (perm[resourceType].validate)
-              for (let [k, v] of Object.entries(perm[resourceType].validate))
+            if (perm[resourceType].validate) {
+              for (const [k, v] of Object.entries(perm[resourceType].validate))
                 funcs[k] = v;
+            }
           } else {
             funcs = {};
           }
         }
+      }
+    }
 
     const validator = (mutationType, mutation, any) => {
       let valid = false;
-      for (let [k, v] of Object.entries(funcs))
+      for (const [k, v] of Object.entries(funcs)) {
         if (v) {
-          let res = validators[k](
+          const res = validators[k](
             resourceType,
             resource,
             mutationType,
@@ -66,6 +68,7 @@ class Authorizer {
           if (res > 0) valid = true;
           else if (res < 0) return false;
         }
+      }
 
       return valid;
     };
diff --git a/common/expression-cnf.js b/common/expression-cnf.js
index 4ed1a34..51960a4 100644
--- a/common/expression-cnf.js
+++ b/common/expression-cnf.js
@@ -7,7 +7,7 @@ function or(cnf1, cnf2) {
   else if (cnf2.length === 0) return cnf1;
 
   if (cnf1.length > cnf2.length) {
-    let c = cnf1;
+    const c = cnf1;
     cnf1 = cnf2;
     cnf2 = c;
   }
@@ -53,10 +53,11 @@ function booleanCnf(exp) {
     return e;
   });
 
-  for (let [k, v] of ranges)
+  for (const [k, v] of ranges) {
     if (k.endsWith(":number"))
       ranges.set(k, Array.from(v).sort((a, b) => a - b));
     else ranges.set(k, Array.from(v).sort());
+  }
 
   const expressions = new Map();
   const mutuallyExclusive = new Map();
@@ -113,11 +114,12 @@ function booleanCnf(exp) {
 
   function getLikeVariables(lhs, pat, esc) {
     const vars = [];
-    let pats = likePatterns.get(lhs);
+    const pats = likePatterns.get(lhs);
     pat = pats.get(`${esc || ""}:${pat}`);
-    for (let p of pats.values())
+    for (const p of pats.values()) {
       if (pat === p || likePatternIncludes(pat, p))
         vars.push(`${lhs}:like:${JSON.stringify(p)}`);
+    }
 
     return vars.map(key => {
       let f = expressions.get(key);
@@ -185,7 +187,7 @@ function booleanCnf(exp) {
         let rhs = JSON.stringify(clause[2]);
         // For consistency
         if (rhs > lhs) {
-          let t = rhs;
+          const t = rhs;
           rhs = lhs;
           lhs = t;
           op = { ">": "<", ">=": "<=", "<": ">", "<=": ">=" }[op] || op;
@@ -218,8 +220,8 @@ function booleanCnf(exp) {
 
   const cnf = recursive(exp, false);
 
-  for (let m of mutuallyExclusive.values()) {
-    let ar = Array.from(m);
+  for (const m of mutuallyExclusive.values()) {
+    const ar = Array.from(m);
     for (let i = 0; i < ar.length; ++i)
       for (let j = i + 1; j < ar.length; ++j) cnf.push([0 - ar[i], 0 - ar[j]]);
   }
diff --git a/common/expression-parser.js b/common/expression-parser.js
index 5d4c541..f581202 100644
--- a/common/expression-parser.js
+++ b/common/expression-parser.js
@@ -4,7 +4,7 @@ const parsimmon = require("parsimmon");
 
 // Turn escaped characters into real ones (e.g. "\\n" becomes "\n").
 function interpretEscapes(str) {
-  let escapes = {
+  const escapes = {
     b: "\b",
     f: "\f",
     n: "\n",
@@ -12,8 +12,8 @@ function interpretEscapes(str) {
     t: "\t"
   };
   return str.replace(/\\(u[0-9a-fA-F]{4}|[^u])/, (_, escape) => {
-    let type = escape.charAt(0);
-    let hex = escape.slice(1);
+    const type = escape.charAt(0);
+    const hex = escape.slice(1);
     if (type === "u") return String.fromCharCode(parseInt(hex, 16));
 
     if (escapes.hasOwnProperty(type)) return escapes[type];
@@ -27,7 +27,7 @@ function map(exp, callback) {
 
   let clone;
   for (let i = 1; i < exp.length; ++i) {
-    let sub = map(exp[i], callback);
+    const sub = map(exp[i], callback);
     if (sub !== exp[i]) {
       clone = clone || exp.slice();
       clone[i] = sub;
@@ -43,7 +43,7 @@ function binaryLeft(operatorsParser, nextParser) {
     parsimmon.seq(operatorsParser, nextParser).many(),
     (first, rest) =>
       rest.reduce((acc, ch) => {
-        let [op, another] = ch;
+        const [op, another] = ch;
         if (Array.isArray(acc) && op === acc[0]) return acc.concat([another]);
         if (Array.isArray(another) && op === another[0])
           return [op, acc].concat(another.slice(1));
@@ -315,8 +315,9 @@ function stringify(exp, level = 0) {
         .join(", ")})`
     );
   } else if (op === "PARAM") {
-    if (typeof exp[1] === "string") return wrap(exp[1]);
-    else if (Array.isArray(exp[1]) && exp[1][0] === "||")
+    if (typeof exp[1] === "string") {
+      return wrap(exp[1]);
+    } else if (Array.isArray(exp[1]) && exp[1][0] === "||") {
       return wrap(
         exp[1]
           .slice(1)
@@ -326,24 +327,27 @@ function stringify(exp, level = 0) {
           })
           .join("")
       );
-    else return wrap(`{${stringify(exp[1])}}`);
+    } else {
+      return wrap(`{${stringify(exp[1])}}`);
+    }
   } else if (op === "IS NULL" || op === "IS NOT NULL") {
     return wrap(`${stringify(exp[1], opLevels[op])} ${op}`);
   } else if (op === "LIKE" || op === "NOT LIKE") {
-    if (exp[3])
+    if (exp[3]) {
       return wrap(
         `${stringify(exp[1], opLevels[op])} ${op} ${stringify(
           exp[2],
           opLevels[op]
         )} ESCAPE ${stringify(exp[3], opLevels[op])}`
       );
-    else
+    } else {
       return wrap(
         `${stringify(exp[1], opLevels[op])} ${op} ${stringify(
           exp[2],
           opLevels[op]
         )}`
       );
+    }
   } else if (op in opLevels) {
     const parts = exp.slice(1).map((e, i) => {
       return stringify(e, opLevels[exp[0]] + Math.min(i - 1, 0));
@@ -357,10 +361,10 @@ function stringify(exp, level = 0) {
 }
 
 function parseLikePattern(pat, esc) {
-  let chars = pat.split("");
+  const chars = pat.split("");
 
   for (let i = 0; i < chars.length; ++i) {
-    let c = chars[i];
+    const c = chars[i];
     if (c === esc) {
       chars[i] = chars[i + 1] || "";
       chars[i + 1] = "";
diff --git a/common/expression.js b/common/expression.js
index 376fce3..49dcc62 100644
--- a/common/expression.js
+++ b/common/expression.js
@@ -8,24 +8,14 @@ const isArray = Array.isArray;
 
 const regExpCache = new WeakMap();
 
-function* permute(arr) {
-  if (arr.length <= 1) {
-    for (let i = 0; i < arr[0]; ++i) yield [i];
-    return;
-  }
-
-  let slc = arr.slice(1);
-  for (let i = 0; i < arr[0]; ++i)
-    for (let innerArr of permute(slc)) yield [i].concat(innerArr);
-}
-
+const REDUCE_SKIP = {};
 function reduce(exp, callback) {
   let loop = true;
   while (loop) {
     loop = false;
     for (let i = 2; i < exp.length; ++i) {
-      let res = callback(exp[i - 1], exp[i]);
-      if (res !== undefined) {
+      const res = callback(exp[i - 1], exp[i]);
+      if (res !== REDUCE_SKIP) {
         loop = true;
         exp = exp.slice();
         exp.splice(i - 1, 2, res);
@@ -71,11 +61,13 @@ function evaluate(exp, obj, now, cb) {
       return reduce(e, (a, b) => {
         if (!isArray(a)) return a ? b : a;
         if (!isArray(b)) return b ? a : b;
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "OR") {
       return reduce(e, (a, b) => {
         if (!isArray(a)) return a ? a : b;
         if (!isArray(b)) return b ? b : a;
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "NOT") {
       if (!isArray(e[1])) return !e[1];
@@ -131,6 +123,7 @@ function evaluate(exp, obj, now, cb) {
           if (a == null || b == null) return null;
           return a * b;
         }
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "/") {
       return reduce(e, (a, b) => {
@@ -138,6 +131,7 @@ function evaluate(exp, obj, now, cb) {
           if (a == null || b == null) return null;
           return a / b;
         }
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "+") {
       return reduce(e, (a, b) => {
@@ -145,6 +139,7 @@ function evaluate(exp, obj, now, cb) {
           if (a == null || b == null) return null;
           return a + b;
         }
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "-") {
       return reduce(e, (a, b) => {
@@ -152,6 +147,7 @@ function evaluate(exp, obj, now, cb) {
           if (a == null || b == null) return null;
           return a - b;
         }
+        return REDUCE_SKIP;
       });
     } else if (e[0] === "||") {
       return reduce(e, (a, b) => {
@@ -159,6 +155,7 @@ function evaluate(exp, obj, now, cb) {
           if (a == null || b == null) return null;
           return `${a}${b}`;
         }
+        return REDUCE_SKIP;
       });
     }
     return e;
@@ -238,7 +235,7 @@ function likePatternToRegExp(pat, esc = "", flags = "") {
 }
 
 function extractParams(exp) {
-  let params = [];
+  const params = [];
   expressionParser.map(exp, e => {
     if (isArray(e) && e[0] === "PARAM") params.push(e[1]);
     return e;
diff --git a/common/sat-solver.js b/common/sat-solver.js
index 815c400..4800345 100644
--- a/common/sat-solver.js
+++ b/common/sat-solver.js
@@ -33,11 +33,12 @@ function satisfiableAt(clauses, varVals, varnr, val) {
 
   // find next unassigned var to split
   let nextVar = 0;
-  for (let i = 1; i < varVals.length; i++)
+  for (let i = 1; i < varVals.length; i++) {
     if (varVals[i] === 0) {
       nextVar = i;
       break;
     }
+  }
 
   if (nextVar === 0) throw new Error("Error in satisfiableAt");
 
@@ -105,7 +106,7 @@ function unitPropagate(clauses, varVals) {
       let unassignedLit = 0; // 0 means none found for this clause
 
       for (let j = 0; j < clause.length; j++) {
-        let lit = clause[j];
+        const lit = clause[j];
         let nr, polarity;
         if (lit < 0) {
           nr = 0 - lit;
@@ -149,7 +150,7 @@ function unitPropagate(clauses, varVals) {
 
     // some units were derived: iterate the main loop
     for (let j = 0; j < derivedQueue.length; j++) {
-      let lit = derivedQueue[j];
+      const lit = derivedQueue[j];
       let nr, polarity;
       if (lit < 0) {
         nr = 0 - lit;
diff --git a/server/api-functions.js b/server/api-functions.js
index 3f46c23..b0acd9d 100644
--- a/server/api-functions.js
+++ b/server/api-functions.js
@@ -6,7 +6,6 @@ const url = require("url");
 
 const config = require("./config");
 const db = require("./db");
-const expression = require("../common/expression");
 const mongodbFunctions = require("./mongodb-functions");
 
 function filterToMongoQuery(filter, negate = false, res = {}) {
@@ -25,7 +24,7 @@ function filterToMongoQuery(filter, negate = false, res = {}) {
     filterToMongoQuery(filter[1], !negate, res);
   } else if (op === "=") {
     const param = filter[1][1];
-    let p = (res[param] = res[param] || {});
+    const p = (res[param] = res[param] || {});
     if (negate) p["$ne"] = filter[2];
     else p["$eq"] = filter[2];
   } else if (op === "<>") {
@@ -69,15 +68,15 @@ function filterToMongoQuery(filter, negate = false, res = {}) {
 
 function deleteResource(resource, id) {
   return new Promise((resolve, reject) => {
-    let resourceUrl =
+    const resourceUrl =
       resource === "virtualParameters" ? "virtual_parameters" : resource;
-    let options = url.parse(
+    const options = url.parse(
       `${config.server.nbi}${resourceUrl}/${encodeURIComponent(id)}`
     );
 
     options.method = "DELETE";
 
-    let _http = options.protocol === "https:" ? https : http;
+    const _http = options.protocol === "https:" ? https : http;
 
     _http
       .request(options, res => {
@@ -91,13 +90,13 @@ function deleteResource(resource, id) {
 }
 
 function postTask(task, connectionRequest, callback) {
-  let options = url.parse(
+  const options = url.parse(
     `${config.server.nbi}devices/${encodeURIComponent(task.device)}/tasks${
       connectionRequest ? "?connection_request" : ""
     }`
   );
   options.method = "POST";
-  let _http = options.protocol === "https:" ? https : http;
+  const _http = options.protocol === "https:" ? https : http;
 
   _http
     .request(options, res => {
@@ -114,14 +113,14 @@ function postTask(task, connectionRequest, callback) {
       });
 
       res.on("end", () => {
-        let buf = new Buffer(bytes);
+        const buf = Buffer.allocUnsafe(bytes);
         let o = 0;
-        for (let c of chunks) {
+        for (const c of chunks) {
           c.copy(buf, o, 0, c.length);
           o += c.length;
         }
         try {
-          let t = JSON.parse(buf);
+          const t = JSON.parse(buf);
           let connectionRequestStatus;
           if (connectionRequest) {
             connectionRequestStatus = "OK";
@@ -144,16 +143,16 @@ function postTask(task, connectionRequest, callback) {
 function postTasks(deviceId, tasks) {
   return new Promise((resolve, reject) => {
     let connectionRequestStatus;
-    let promises = [];
-    for (let [idx, task] of tasks.entries()) {
+    const promises = [];
+    for (const [idx, task] of tasks.entries()) {
       task.device = deviceId;
       promises.push(
         new Promise((res, rej) => {
-          let conReq = idx === tasks.length - 1;
+          const conReq = idx === tasks.length - 1;
           delete task._id;
           task.expiry = 5;
           postTask(task, conReq, (err, t, crs) => {
-            if (err) return rej(err);
+            if (err) return void rej(err);
             if (conReq) connectionRequestStatus = crs;
             res({ _id: t._id, status: "pending" });
           });
@@ -163,14 +162,15 @@ function postTasks(deviceId, tasks) {
 
     Promise.all(promises)
       .then(statuses => {
-        if (connectionRequestStatus !== "OK")
-          return resolve({
+        if (connectionRequestStatus !== "OK") {
+          return void resolve({
             connectionRequest: connectionRequestStatus,
             tasks: statuses
           });
+        }
 
-        let promises2 = [];
-        for (let s of statuses) {
+        const promises2 = [];
+        for (const s of statuses) {
           promises2.push(db.query("tasks", ["=", ["PARAM", "_id"], s._id]));
           promises2.push(
             db.query("faults", [
@@ -183,7 +183,7 @@ function postTasks(deviceId, tasks) {
 
         Promise.all(promises2)
           .then(res => {
-            for (let [i, r] of statuses.entries()) {
+            for (const [i, r] of statuses.entries()) {
               if (res[i * 2].length === 0) {
                 r.status = "done";
               } else if (res[i * 2 + 1].length === 1) {
@@ -216,7 +216,7 @@ function updateTags(deviceId, tags) {
           );
           if (onOff) options.method = "POST";
           else options.method = "DELETE";
-          let _http = options.protocol === "https:" ? https : http;
+          const _http = options.protocol === "https:" ? https : http;
 
           _http
             .request(options, res => {
@@ -237,17 +237,19 @@ function ping(host) {
       `${config.server.nbi}ping/${encodeURIComponent(host)}`
     );
 
-    let _http = options.protocol === "https:" ? https : http;
+    const _http = options.protocol === "https:" ? https : http;
     _http
       .request(options, res => {
         if (res.statusCode === 404) {
           res.resume();
-          return resolve({});
+          return void resolve({});
         }
 
         if (res.statusCode !== 200) {
           res.resume();
-          return reject(new Error(`Unexpected status code ${res.statusCode}`));
+          return void reject(
+            new Error(`Unexpected status code ${res.statusCode}`)
+          );
         }
 
         const chunks = [];
@@ -258,18 +260,19 @@ function ping(host) {
         });
 
         res.on("end", () => {
-          let buf = new Buffer(bytes);
+          const buf = Buffer.allocUnsafe(bytes);
           let o = 0;
-          for (let c of chunks) {
+          for (const c of chunks) {
             c.copy(buf, o, 0, c.length);
             o += c.length;
           }
-          let m = buf
+          const m = buf
             .toString()
             .match(
               /(\d) packets transmitted, (\d) received, ([\d.%]+) packet loss[^]*([\d.]+)\/([\d.]+)\/([\d.]+)\/([\d.]+)/
             );
-          if (!m) return reject(new Error("Could not parse ping response"));
+          if (!m)
+            return void reject(new Error("Could not parse ping response"));
 
           resolve({
             packetsTransmitted: +m[1],
@@ -288,15 +291,15 @@ function ping(host) {
 
 function putResource(resource, id, data) {
   return new Promise((resolve, reject) => {
-    let resourceUrl =
+    const resourceUrl =
       resource === "virtualParameters" ? "virtual_parameters" : resource;
-    let options = url.parse(
+    const options = url.parse(
       `${config.server.nbi}${resourceUrl}/${encodeURIComponent(id)}`
     );
 
     options.method = "PUT";
 
-    let _http = options.protocol === "https:" ? https : http;
+    const _http = options.protocol === "https:" ? https : http;
 
     if (resource === "presets") data = mongodbFunctions.preProcessPreset(data);
 
@@ -306,7 +309,7 @@ function putResource(resource, id, data) {
     if (resource === "virtualParameters")
       data = mongodbFunctions.preProcessVirtualParameters(data);
 
-    let body = typeof data !== "string" ? JSON.stringify(data) : data;
+    const body = typeof data !== "string" ? JSON.stringify(data) : data;
     _http
       .request(options, res => {
         const chunks = [];
@@ -317,14 +320,16 @@ function putResource(resource, id, data) {
         });
 
         res.on("end", () => {
-          if (res.statusCode === 200) return resolve();
-          else if (res.statusCode !== 400)
-            return reject(
+          if (res.statusCode === 200) {
+            return void resolve();
+          } else if (res.statusCode !== 400) {
+            return void reject(
               new Error(`Unexpected status code ${res.statusCode}`)
             );
-          let buf = new Buffer(bytes);
+          }
+          const buf = Buffer.allocUnsafe(bytes);
           let o = 0;
-          for (let c of chunks) {
+          for (const c of chunks) {
             c.copy(buf, o, 0, c.length);
             o += c.length;
           }
@@ -337,17 +342,22 @@ function putResource(resource, id, data) {
 
 function putFile(id, metadata, fileStream) {
   return new Promise((resolve, reject) => {
-    let options = url.parse(
+    const options = url.parse(
       `${config.server.nbi}files/${encodeURIComponent(id)}`
     );
 
     options.method = "PUT";
     options.headers = Object.assign({}, metadata);
-    let _http = options.protocol === "https:" ? https : http;
-    let req = _http.request(options, res => {
+    const _http = options.protocol === "https:" ? https : http;
+    const req = _http.request(options, res => {
       res.resume();
-      if (res.statusCode === 201) return resolve();
-      else return reject(new Error(`Unexpected status code ${res.statusCode}`));
+      if (res.statusCode === 201) {
+        return void resolve();
+      } else {
+        return void reject(
+          new Error(`Unexpected status code ${res.statusCode}`)
+        );
+      }
     });
     fileStream.pipe(req);
   });
diff --git a/server/api.js b/server/api.js
index dd1cd3c..f76ba65 100644
--- a/server/api.js
+++ b/server/api.js
@@ -2,7 +2,6 @@
 
 const zlib = require("zlib");
 const Router = require("koa-router");
-const config = require("./config");
 const db = require("./db");
 const apiFunctions = require("./api-functions");
 const expression = require("../common/expression");
@@ -38,7 +37,7 @@ const resources = {
   tasks: 0
 };
 
-for (let [resource, flags] of Object.entries(resources)) {
+for (const [resource, flags] of Object.entries(resources)) {
   router.head(`/${resource}`, async (ctx, next) => {
     let filter = true;
     if (ctx.request.query.filter)
@@ -52,17 +51,18 @@ for (let [resource, flags] of Object.entries(resources)) {
 
     if (!ctx.state.authorizer.hasAccess(resource, 1)) {
       logUnauthorizedWarning(log);
-      return next();
+      return void next();
     }
 
     // Exclude temporary tasks and faults
-    if (resource === "tasks" || resource === "faults")
+    if (resource === "tasks" || resource === "faults") {
       filter = expression.and(filter, [
         "NOT",
         ["<", ["PARAM", "expiry"], Date.now() + 60000]
       ]);
+    }
 
-    let count = await db.count(resource, filter);
+    const count = await db.count(resource, filter);
 
     ctx.set("X-Total-Count", count);
     ctx.body = "";
@@ -72,7 +72,7 @@ for (let [resource, flags] of Object.entries(resources)) {
   });
 
   router.get(`/${resource}`, async (ctx, next) => {
-    let options = {};
+    const options = {};
     let filter = true;
     if (ctx.request.query.filter)
       filter = expression.parse(ctx.request.query.filter);
@@ -80,10 +80,11 @@ for (let [resource, flags] of Object.entries(resources)) {
     if (ctx.request.query.skip) options.skip = +ctx.request.query.skip;
     if (ctx.request.query.sort)
       options.sort = JSON.parse(ctx.request.query.sort);
-    if (ctx.request.query.projection)
+    if (ctx.request.query.projection) {
       options.projection = ctx.request.query.projection
         .split(",")
         .reduce((obj, k) => Object.assign(obj, { [k]: 1 }), {});
+    }
 
     const log = {
       message: `Query ${resource}`,
@@ -97,15 +98,16 @@ for (let [resource, flags] of Object.entries(resources)) {
 
     if (!ctx.state.authorizer.hasAccess(resource, 2)) {
       logUnauthorizedWarning(log);
-      return next();
+      return void next();
     }
 
     // Exclude temporary tasks and faults
-    if (resource === "tasks" || resource === "faults")
+    if (resource === "tasks" || resource === "faults") {
       filter = expression.and(filter, [
         "NOT",
         ["<", ["PARAM", "expiry"], Date.now() + 60000]
       ]);
+    }
 
     let stream;
     switch (ctx.acceptsEncodings("gzip", "deflate", "identity")) {
@@ -139,7 +141,7 @@ for (let [resource, flags] of Object.entries(resources)) {
 
   // CSV download
   router.get(`/${resource}.csv`, async (ctx, next) => {
-    let options = { projection: {} };
+    const options = { projection: {} };
     let filter = true;
     if (ctx.request.query.filter)
       filter = expression.parse(ctx.request.query.filter);
@@ -159,28 +161,25 @@ for (let [resource, flags] of Object.entries(resources)) {
 
     if (!ctx.state.authorizer.hasAccess(resource, 2)) {
       logUnauthorizedWarning(log);
-      return next();
+      return void next();
     }
 
     const columns = JSON.parse(ctx.request.query.columns);
     const now = Date.now();
 
-    for (let [k, v] of Object.entries(columns)) {
-      const e = expression.evaluate(
-        expression.parse(v),
-        null,
-        now
-      );
+    for (const [k, v] of Object.entries(columns)) {
+      const e = expression.evaluate(expression.parse(v), null, now);
       columns[k] = e;
-      for (let p of expression.extractParams(e)) options.projection[p] = 1;
+      for (const p of expression.extractParams(e)) options.projection[p] = 1;
     }
 
     // Exclude temporary tasks and faults
-    if (resource === "tasks" || resource === "faults")
+    if (resource === "tasks" || resource === "faults") {
       filter = expression.and(filter, [
         "NOT",
         ["<", ["PARAM", "expiry"], Date.now() + 60000]
       ]);
+    }
 
     let stream;
     switch (ctx.acceptsEncodings("gzip", "deflate", "identity")) {
@@ -209,24 +208,26 @@ for (let [resource, flags] of Object.entries(resources)) {
       Object.keys(columns).map(k => `"${k.replace(/"/, '""')}"`) + "\n"
     );
     await db.query(resource, filter, options, obj => {
-      let arr = Object.values(columns).map(exp => {
-        let v = expression.evaluate(exp, obj, null, e => {
-          if (Array.isArray(e))
+      const arr = Object.values(columns).map(exp => {
+        const v = expression.evaluate(exp, obj, null, e => {
+          if (Array.isArray(e)) {
             if (e[0] === "PARAM") {
               if (resource === "devices") {
                 if (e[1] === "Tags") {
-                  let tags = [];
-                  for (let p in obj)
+                  const tags = [];
+                  for (const p in obj)
                     if (p.startsWith("Tags.")) tags.push(p.slice(5));
 
                   return tags.join(", ");
                 }
               }
             } else if (e[0] === "FUNC") {
-              if (e[1] === "DATE_STRING")
+              if (e[1] === "DATE_STRING") {
                 if (e[2] && !Array.isArray(e[2]))
                   return new Date(e[2]).toISOString();
+              }
             }
+          }
 
           return e;
         });
@@ -249,15 +250,15 @@ for (let [resource, flags] of Object.entries(resources)) {
       filter: `${RESOURCE_IDS[resource]} = "${ctx.params.id}"`
     };
 
-    let filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
+    const filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
     if (!ctx.state.authorizer.hasAccess(resource, 2)) {
       logUnauthorizedWarning(log);
-      return next();
+      return void next();
     }
 
-    let res = await db.query(resource, filter);
+    const res = await db.query(resource, filter);
 
-    if (!res.length) return next();
+    if (!res.length) return void next();
 
     logger.accessInfo(log);
     ctx.body = "";
@@ -270,22 +271,22 @@ for (let [resource, flags] of Object.entries(resources)) {
       filter: `${RESOURCE_IDS[resource]} = "${ctx.params.id}"`
     };
 
-    let filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
+    const filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
     if (!ctx.state.authorizer.hasAccess(resource, 2)) {
       logUnauthorizedWarning(log);
-      return next();
+      return void next();
     }
 
-    let res = await db.query(resource, filter);
+    const res = await db.query(resource, filter);
 
-    if (!res.length) return next();
+    if (!res.length) return void next();
 
     logger.accessInfo(log);
     ctx.body = res[0];
   });
 
   // TODO add PUT, PATCH routes
-  if (flags & RESOURCE_DELETE)
+  if (flags & RESOURCE_DELETE) {
     router.delete(`/${resource}/:id`, async (ctx, next) => {
       const log = {
         message: `Delete ${resource}`,
@@ -294,18 +295,18 @@ for (let [resource, flags] of Object.entries(resources)) {
       };
 
       const authorizer = ctx.state.authorizer;
-      let filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
+      const filter = ["=", ["PARAM", RESOURCE_IDS[resource]], ctx.params.id];
       if (!authorizer.hasAccess(resource, 2)) {
         logUnauthorizedWarning(log);
-        return next();
+        return void next();
       }
-      let res = await db.query(resource, filter);
-      if (!res.length) return next();
+      const res = await db.query(resource, filter);
+      if (!res.length) return void next();
 
       const validate = authorizer.getValidator(resource, res[0]);
       if (!validate("delete")) {
         logUnauthorizedWarning(log);
-        return (ctx.status = 403);
+        return void (ctx.status = 403);
       }
 
       await apiFunctions.deleteResource(resource, ctx.params.id);
@@ -314,8 +315,9 @@ for (let [resource, flags] of Object.entries(resources)) {
 
       ctx.body = "";
     });
+  }
 
-  if (flags & RESOURCE_PUT)
+  if (flags & RESOURCE_PUT) {
     router.put(`/${resource}/:id`, async (ctx, next) => {
       const id = ctx.params.id;
 
@@ -328,30 +330,31 @@ for (let [resource, flags] of Object.entries(resources)) {
       const authorizer = ctx.state.authorizer;
       if (!authorizer.hasAccess(resource, 3)) {
         logUnauthorizedWarning(log);
-        return next();
+        return void next();
       }
 
-      let obj = ctx.request.body;
+      const obj = ctx.request.body;
 
       const validate = authorizer.getValidator(resource, obj);
       if (!validate("put")) {
         logUnauthorizedWarning(log);
-        return (ctx.status = 403);
+        return void (ctx.status = 403);
       }
 
-      let err = await apiFunctions.putResource(resource, id, obj);
+      const err = await apiFunctions.putResource(resource, id, obj);
 
       if (err) {
         log.message += " failed";
         logger.accessWarn(log);
         ctx.body = err;
-        return (ctx.status = 400);
+        return void (ctx.status = 400);
       }
 
       logger.accessInfo(log);
 
       ctx.body = "";
     });
+  }
 }
 
 router.put("/files/:id", async (ctx, next) => {
@@ -367,10 +370,10 @@ router.put("/files/:id", async (ctx, next) => {
   const authorizer = ctx.state.authorizer;
   if (!authorizer.hasAccess(resource, 3)) {
     logUnauthorizedWarning(log);
-    return next();
+    return void next();
   }
 
-  let metadata = {
+  const metadata = {
     fileType: ctx.request.headers["metadata.filetype"] || "",
     oui: ctx.request.headers["metadata.oui"] || "",
     productClass: ctx.request.headers["metadata.productclass"] || "",
@@ -380,16 +383,16 @@ router.put("/files/:id", async (ctx, next) => {
   const validate = authorizer.getValidator(resource, metadata);
   if (!validate("put")) {
     logUnauthorizedWarning(log);
-    return (ctx.status = 403);
+    return void (ctx.status = 403);
   }
 
-  let err = await apiFunctions.putFile(id, metadata, ctx.req);
+  const err = await apiFunctions.putFile(id, metadata, ctx.req);
 
   if (err) {
     log.message += " failed";
     logger.accessWarn(log);
     ctx.body = err;
-    return (ctx.status = 400);
+    return void (ctx.status = 400);
   }
 
   log.metadata = metadata;
@@ -406,22 +409,23 @@ router.post("/devices/:id/tasks", async (ctx, next) => {
   };
 
   const authorizer = ctx.state.authorizer;
-  let filter = ["=", ["PARAM", "DeviceID.ID"], ctx.params.id];
+  const filter = ["=", ["PARAM", "DeviceID.ID"], ctx.params.id];
   if (!authorizer.hasAccess("devices", 2)) {
     logUnauthorizedWarning(log);
-    return next();
+    return void next();
   }
-  let devices = await db.query("devices", filter);
-  if (!devices.length) return next();
+  const devices = await db.query("devices", filter);
+  if (!devices.length) return void next();
 
   const validate = authorizer.getValidator("devices", devices[0]);
-  for (let t of ctx.request.body)
+  for (const t of ctx.request.body) {
     if (!validate("task", t)) {
       logUnauthorizedWarning(log);
-      return (ctx.status = 403);
+      return void (ctx.status = 403);
     }
+  }
 
-  let res = await apiFunctions.postTasks(ctx.params.id, ctx.request.body);
+  const res = await apiFunctions.postTasks(ctx.params.id, ctx.request.body);
 
   log.tasks = res.tasks.map(t => t._id).join(",");
 
@@ -440,18 +444,18 @@ router.post("/devices/:id/tags", async (ctx, next) => {
   };
 
   const authorizer = ctx.state.authorizer;
-  let filter = ["=", ["PARAM", "DeviceID.ID"], ctx.params.id];
+  const filter = ["=", ["PARAM", "DeviceID.ID"], ctx.params.id];
   if (!authorizer.hasAccess("devices", 2)) {
     logUnauthorizedWarning(log);
-    return next();
+    return void next();
   }
-  let res = await db.query("devices", filter);
-  if (!res.length) return next();
+  const res = await db.query("devices", filter);
+  if (!res.length) return void next();
 
   const validate = authorizer.getValidator("devices", res[0]);
   if (!validate("tags", ctx.request.body)) {
     logUnauthorizedWarning(log);
-    return (ctx.status = 403);
+    return void (ctx.status = 403);
   }
 
   await apiFunctions.updateTags(ctx.params.id, ctx.request.body);
diff --git a/server/config.js b/server/config.js
index 4dee41d..3b7ee4c 100644
--- a/server/config.js
+++ b/server/config.js
@@ -3,7 +3,7 @@
 const fs = require("fs");
 const configFile = JSON.parse(fs.readFileSync("./config.json"));
 
-let config;
+const config = loadConfig(configFile);
 
 function getClientConfig() {
   return Object.assign({}, config, {
@@ -33,6 +33,4 @@ function loadConfig(conf, root = {}) {
   return root;
 }
 
-config = loadConfig(configFile);
-
 module.exports = Object.assign({}, config, { getClientConfig });
diff --git a/server/db.js b/server/db.js
index 153160b..c1180f1 100644
--- a/server/db.js
+++ b/server/db.js
@@ -22,18 +22,19 @@ const RESOURCE_COLLECTION = {
 };
 
 function getClient() {
-  if (!_clientPromise)
+  if (!_clientPromise) {
     _clientPromise = new Promise((resolve, reject) => {
       const CONNECTION_URL = config.server.mongodbConnectionUrl;
       mongodb.MongoClient.connect(
         CONNECTION_URL,
         { useNewUrlParser: true },
         (err, client) => {
-          if (err) return reject(err);
+          if (err) return void reject(err);
           resolve(client);
         }
       );
     });
+  }
 
   return _clientPromise;
 }
@@ -61,12 +62,13 @@ function query(resource, filter, options, callback) {
         .db(RESOURCE_DB[resource])
         .collection(RESOURCE_COLLECTION[resource] || resource);
       const cursor = collection.find(q);
-      if (options.projection)
+      if (options.projection) {
         cursor.project(
           resource === "devices"
             ? mongodbFunctions.processDeviceProjection(options.projection)
             : options.projection
         );
+      }
       if (options.skip) cursor.skip(options.skip);
       if (options.limit) cursor.limit(options.limit);
 
@@ -83,7 +85,7 @@ function query(resource, filter, options, callback) {
         cursor.sort(s);
       }
 
-      if (!callback)
+      if (!callback) {
         cursor.toArray((err, docs) => {
           if (err) return reject(err);
           if (resource === "devices")
@@ -98,7 +100,7 @@ function query(resource, filter, options, callback) {
             docs = docs.map(d => mongodbFunctions.flattenFile(d));
           return resolve(docs);
         });
-      else
+      } else {
         cursor.forEach(
           doc => {
             if (resource === "devices")
@@ -118,6 +120,7 @@ function query(resource, filter, options, callback) {
             else resolve();
           }
         );
+      }
     });
   });
 }
@@ -152,10 +155,11 @@ function count(resource, filter) {
 }
 
 function disconnect() {
-  if (_clientPromise)
+  if (_clientPromise) {
     _clientPromise.then(client => {
       client.close();
     });
+  }
 }
 
 exports.query = query;
diff --git a/server/logger.js b/server/logger.js
index aab3345..80e314b 100644
--- a/server/logger.js
+++ b/server/logger.js
@@ -153,9 +153,10 @@ function formatSimple(details, systemd) {
   flatten(details);
 
   let remote = "";
-  if (details.remoteAddress)
+  if (details.remoteAddress) {
     if (details.user) remote = `${details.user}@${details.remoteAddress}: `;
     else remote = `${details.remoteAddress}: `;
+  }
 
   const keys = Object.keys(details);
   const skip = {
@@ -168,8 +169,8 @@ function formatSimple(details, systemd) {
 
   let meta = "";
 
-  let kv = [];
-  for (let k of keys)
+  const kv = [];
+  for (const k of keys)
     if (!skip[k]) kv.push(`${k}=${JSON.stringify(details[k])}`);
 
   if (kv.length) meta = `; ${kv.join(" ")}`;
diff --git a/server/mongodb-functions.js b/server/mongodb-functions.js
index 80a626d..e002720 100644
--- a/server/mongodb-functions.js
+++ b/server/mongodb-functions.js
@@ -44,7 +44,7 @@ function processDeviceFilter(filter) {
       });
 
       if (typeof e[2] === "number") {
-        let alt = e.slice();
+        const alt = e.slice();
         alt[2] = new Date(e[2]);
         e = ["OR", e, alt];
       }
@@ -58,7 +58,7 @@ function processTasksFilter(filter) {
   return expressionParser.map(filter, exp => {
     if (!Array.isArray(exp)) return exp;
     if (["=", "<>", ">", ">=", "<", "<="].includes(exp[0])) {
-      let e = exp.slice();
+      const e = exp.slice();
       if (e[1][0] === "PARAM" && e[1][1] === "_id")
         e[2] = new mongodb.ObjectID(e[2]);
       else if (e[1][0] === "PARAM" && e[1][1] === "timestamp")
@@ -75,7 +75,7 @@ function processFaultsFilter(filter) {
   return expressionParser.map(filter, exp => {
     if (!Array.isArray(exp)) return exp;
     if (["=", "<>", ">", ">=", "<", "<="].includes(exp[0])) {
-      let e = exp.slice();
+      const e = exp.slice();
       if (e[1][0] === "PARAM" && e[1][1] === "timestamp") e[2] = new Date(e[2]);
       else if (e[1][0] === "PARAM" && e[1][1] === "expiry")
         e[2] = new Date(e[2]);
@@ -101,7 +101,7 @@ function filterToMongoQuery(filter, negate = false, res = {}) {
     filterToMongoQuery(filter[1], !negate, res);
   } else if (op === "=") {
     const param = filter[1][1];
-    let p = (res[param] = res[param] || {});
+    const p = (res[param] = res[param] || {});
     if (negate) p["$ne"] = filter[2];
     else p["$eq"] = filter[2];
   } else if (op === "<>") {
@@ -141,17 +141,19 @@ function filterToMongoQuery(filter, negate = false, res = {}) {
     let param;
     let flags;
     if (filter[1][0] === "FUNC" && filter[1][1] === "UPPER") {
-      if (filter[2] !== filter[2].toUpperCase())
+      if (filter[2] !== filter[2].toUpperCase()) {
         throw new Error(
           "Cannot compare UPPER() against non upper case pattern"
         );
+      }
       param = filter[1][2][1];
       flags = "i";
     } else if (filter[1][0] === "FUNC" && filter[1][1] === "LOWER") {
-      if (filter[2] !== filter[2].toLowerCase())
+      if (filter[2] !== filter[2].toLowerCase()) {
         throw new Error(
           "Cannot compare LOWER() against non lower case pattern"
         );
+      }
       param = filter[1][2][1];
       flags = "i";
     } else {
@@ -171,7 +173,7 @@ function filterToMongoQuery(filter, negate = false, res = {}) {
 function processDeviceProjection(projection) {
   if (!projection) return projection;
   const p = {};
-  for (const [k, v] of Object.entries(projection))
+  for (const [k, v] of Object.entries(projection)) {
     if (k === "DeviceID.ID") {
       p["_id"] = 1;
     } else if (k.startsWith("DeviceID")) {
@@ -189,6 +191,7 @@ function processDeviceProjection(projection) {
     } else {
       p[k] = v;
     }
+  }
 
   return p;
 }
@@ -196,18 +199,19 @@ function processDeviceProjection(projection) {
 function processDeviceSort(sort) {
   if (!sort) return sort;
   const s = {};
-  for (const [k, v] of Object.entries(sort))
+  for (const [k, v] of Object.entries(sort)) {
     if (k === "DeviceID.ID") s["_id"] = v;
     else if (k === "Events.Inform") s["_lastInform"] = v;
     else s[k] = v;
+  }
 
   return s;
 }
 
 function flattenDevice(device) {
   function recursive(input, root, output, timestamp) {
-    for (let [name, tree] of Object.entries(input)) {
-      if (!root)
+    for (const [name, tree] of Object.entries(input)) {
+      if (!root) {
         if (name === "_lastInform") {
           output["Events.Inform"] = {
             value: [Date.parse(tree), "xsd:dateTime"],
@@ -294,7 +298,7 @@ function flattenDevice(device) {
             objectTimestamp: timestamp
           };
 
-          for (let t of tree)
+          for (const t of tree) {
             output[`Tags.${t}`] = {
               value: [true, "xsd:boolean"],
               valueTimestamp: timestamp,
@@ -303,7 +307,9 @@ function flattenDevice(device) {
               object: false,
               objectTimestamp: timestamp
             };
+          }
         }
+      }
 
       if (name.startsWith("_")) continue;
 
@@ -329,7 +335,7 @@ function flattenDevice(device) {
         attrs["writableTimestamp"] = childrenTimestamp;
       }
 
-      let r = root ? `${root}.${name}` : name;
+      const r = root ? `${root}.${name}` : name;
       output[r] = attrs;
 
       if (attrs["object"] || tree["object"] == null)
@@ -348,14 +354,14 @@ function flattenFault(fault) {
   if (f.timestamp) f.timestamp = +f.timestamp;
   if (f.expiry) f.expiry = +f.expiry;
   if (f.detail) {
-    for (let [k, v] of Object.entries(f.detail)) fault[`detail.${k}`] = v;
+    for (const [k, v] of Object.entries(f.detail)) fault[`detail.${k}`] = v;
     delete f.detail;
   }
   return f;
 }
 
 function flattenTask(task) {
-  let t = Object.assign({}, task);
+  const t = Object.assign({}, task);
   t._id = "" + t._id;
   if (t.timestamp) t.timestamp = +t.timestamp;
   if (t.expiry) t.expiry = +t.expiry;
@@ -363,20 +369,21 @@ function flattenTask(task) {
 }
 
 function mongoQueryToFilter(query) {
-  let expressions = [];
+  const expressions = [];
   function recursive(_query) {
-    for (let [k, v] of Object.entries(_query))
+    for (const [k, v] of Object.entries(_query)) {
       if (k[0] == "$") {
-        if (k == "$and") for (let vv of Object.values(v)) recursive(vv);
+        if (k == "$and") for (const vv of Object.values(v)) recursive(vv);
         else throw new Error(`Operator ${k} not supported`);
       } else if (k == "_tags") {
         if (typeof v === "object") {
           if (Array.isArray(v)) throw new Error(`Invalid type`);
 
-          for (let [kk, vv] of Object.entries(v))
+          for (const [kk, vv] of Object.entries(v)) {
             if (kk == "$ne")
               expressions.push(["IS NULL", ["PARAM", `Tags.${vv}`]]);
             else throw new Error(`Operator ${kk} not supported`);
+          }
         } else {
           expressions.push(["IS NOT NULL", ["PARAM", `Tags.${v}`]]);
         }
@@ -388,7 +395,7 @@ function mongoQueryToFilter(query) {
       } else if (typeof v === "object") {
         if (Array.isArray(v)) throw new Error(`Invalid type`);
 
-        for (let [kk, vv] of Object.entries(v)) {
+        for (const [kk, vv] of Object.entries(v)) {
           let op;
           switch (kk) {
             case "$eq":
@@ -417,6 +424,7 @@ function mongoQueryToFilter(query) {
       } else {
         expressions.push(["=", ["PARAM", k], v]);
       }
+    }
   }
   recursive(query);
 
@@ -428,7 +436,7 @@ function mongoQueryToFilter(query) {
 }
 
 function flattenPreset(preset) {
-  let p = Object.assign({}, preset);
+  const p = Object.assign({}, preset);
   if (p.precondition) {
     p.precondition = mongoQueryToFilter(JSON.parse(p.precondition));
     p.precondition = p.precondition.length
@@ -437,12 +445,12 @@ function flattenPreset(preset) {
   }
 
   if (p.events) {
-    let e = [];
-    for (let [k, v] of Object.entries(p.events)) e.push(v ? k : `-${k}`);
+    const e = [];
+    for (const [k, v] of Object.entries(p.events)) e.push(v ? k : `-${k}`);
     p.events = e.join(", ");
   }
 
-  let provision = p.configurations[0];
+  const provision = p.configurations[0];
   if (
     p.configurations.length != 1 ||
     provision.type != "provision" ||
@@ -459,7 +467,7 @@ function flattenPreset(preset) {
 }
 
 function flattenFile(file) {
-  let f = {};
+  const f = {};
   f["_id"] = file["_id"];
   if (file.metadata) {
     f["metadata.fileType"] = file.metadata.fileType || "";
@@ -471,14 +479,14 @@ function flattenFile(file) {
 }
 
 function preProcessPreset(data) {
-  let preset = Object.assign({}, data);
+  const preset = Object.assign({}, data);
   preset.precondition = preset.precondition
     ? filterToMongoQuery(expression.parse(preset.precondition))
     : {};
   preset.precondition = JSON.stringify(preset.precondition);
 
-  let events = {};
-  if (preset.events)
+  const events = {};
+  if (preset.events) {
     for (let e of preset.events.split(",")) {
       let v = true;
       e = e.trim();
@@ -488,12 +496,13 @@ function preProcessPreset(data) {
       }
       if (e) events[e] = v;
     }
+  }
 
   preset.events = events;
 
   if (!preset.provision) throw new Error("Invalid preset provision");
 
-  let configuration = {
+  const configuration = {
     type: "provision",
     name: preset.provision
   };
diff --git a/server/server.js b/server/server.js
index 012230c..6e5b808 100644
--- a/server/server.js
+++ b/server/server.js
@@ -42,11 +42,10 @@ function getPermissionSets(roles) {
             "virtualParameters",
             "files"
           ].includes(k)
-        )
+        ) {
           if (v.filter == null || v.filter === "") v.filter = true;
-          else {
-            v.filter = expression.parse(v.filter);
-          }
+          else v.filter = expression.parse(v.filter);
+        }
       }
       return p;
     });
@@ -76,11 +75,13 @@ koa.use(
 );
 
 koa.use(async (ctx, next) => {
-  if (ctx.state.user && ctx.state.user.roles)
+  if (ctx.state.user && ctx.state.user.roles) {
     ctx.state.authorizer = new Authorizer(
       getPermissionSets(ctx.state.user.roles)
     );
-  else ctx.state.authorizer = new Authorizer([]);
+  } else {
+    ctx.state.authorizer = new Authorizer([]);
+  }
 
   return next();
 });
@@ -89,7 +90,7 @@ router.post("/login", async ctx => {
   const username = ctx.request.body.username;
   const password = ctx.request.body.password;
 
-  let log = {
+  const log = {
     message: "Log in",
     context: ctx,
     username: username
@@ -110,10 +111,9 @@ router.post("/login", async ctx => {
     logger.accessWarn(log);
   }
 
-  let roles;
-  roles = await authSimple(username, password);
+  const roles = await authSimple(username, password);
 
-  if (roles) return success(roles, "simple");
+  if (roles) return void success(roles, "simple");
 
   failure();
 });
@@ -172,7 +172,7 @@ koa.use(
 koa.use(router.routes());
 koa.use(koaStatic("./public"));
 
-let server = http
+const server = http
   .createServer(koa.callback())
   .listen(config.server.port, config.server.interface);