Convert backend code to ES modules

Bundling code now with Rollup for its flat bundling and tree shaking
support. Front end code still goes through Webpack for browser support.

lib/ui/db.js

@@ -1,9 +1,9 @@
 "use strict";
 
-const mongodb = require("mongodb");
-const config = require("../config");
-const mongodbFunctions = require("./mongodb-functions");
-const expression = require("../common/expression");
+import { MongoClient } from "mongodb";
+import * as config from "../config";
+import * as mongodbFunctions from "./mongodb-functions";
+import * as expression from "../common/expression";
 
 const CACHE_TTL = 300000;
 
@@ -24,7 +24,7 @@ function getClient() {
   if (!_clientPromise) {
     _clientPromise = new Promise((resolve, reject) => {
       const CONNECTION_URL = config.get("MONGODB_CONNECTION_URL");
-      mongodb.MongoClient.connect(
+      MongoClient.connect(
         CONNECTION_URL,
         { useNewUrlParser: true },
         (err, client) => {
@@ -39,7 +39,7 @@ function getClient() {
   return _clientPromise;
 }
 
-function cache(key, valueGetter, ttl) {
+export function cache(key, valueGetter, ttl) {
   return new Promise((resolve, reject) => {
     getClient()
       .then(client => {
@@ -72,7 +72,7 @@ function cache(key, valueGetter, ttl) {
   });
 }
 
-function query(resource, filter, options, callback) {
+export function query(resource, filter, options, callback) {
   options = options || {};
   let q;
   filter = expression.evaluate(filter, null, Date.now());
@@ -158,7 +158,7 @@ function query(resource, filter, options, callback) {
   });
 }
 
-function count(resource, filter) {
+export function count(resource, filter) {
   let q;
   filter = expression.evaluate(filter, null, Date.now());
 
@@ -187,15 +187,10 @@ function count(resource, filter) {
   });
 }
 
-function disconnect() {
+export function disconnect() {
   if (_clientPromise) {
     _clientPromise.then(client => {
       client.close();
     });
   }
 }
-
-exports.query = query;
-exports.count = count;
-exports.cache = cache;
-exports.disconnect = disconnect;