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/cache.js

@@ -18,7 +18,8 @@
  */
 "use strict";
 
-const config = require("./config");
+import { MongoClient } from "mongodb";
+import * as config from "./config";
 
 const MAX_CACHE_TTL = config.get("MAX_CACHE_TTL");
 
@@ -26,11 +27,10 @@ let mongoClient;
 let mongoCollection;
 let mongoTimeOffset = 0;
 
-function connect(callback) {
-  const mongodb = require("mongodb");
+export function connect(callback) {
   const MONGODB_CONNECTION_URL = config.get("MONGODB_CONNECTION_URL");
 
-  mongodb.MongoClient.connect(
+  MongoClient.connect(
     MONGODB_CONNECTION_URL,
     { useNewUrlParser: true },
     (err, client) => {
@@ -51,11 +51,11 @@ function connect(callback) {
   );
 }
 
-function disconnect() {
+export function disconnect() {
   if (mongoClient) mongoClient.close();
 }
 
-function get(key, callback) {
+export function get(key, callback) {
   const expire = new Date(Date.now() - mongoTimeOffset);
   if (Array.isArray(key)) {
     mongoCollection.find({ _id: { $in: key } }).toArray((err, res) => {
@@ -83,13 +83,13 @@ function get(key, callback) {
   }
 }
 
-function del(key, callback) {
+export function del(key, callback) {
   if (Array.isArray(key))
     mongoCollection.deleteMany({ _id: { $in: key } }, callback);
   else mongoCollection.deleteOne({ _id: key }, callback);
 }
 
-function set(key, value, ttl, callback) {
+export function set(key, value, ttl, callback) {
   if (!callback && typeof v === "function") {
     callback = ttl;
     ttl = null;
@@ -106,7 +106,7 @@ function set(key, value, ttl, callback) {
   );
 }
 
-function pop(key, callback) {
+export function pop(key, callback) {
   mongoCollection.findOneAndDelete({ _id: key }, (err, res) => {
     if (err || !res["value"]) return void callback(err);
 
@@ -117,7 +117,7 @@ function pop(key, callback) {
   });
 }
 
-function lock(lockName, ttl, callback) {
+export function lock(lockName, ttl, callback) {
   const token = Math.random()
     .toString(36)
     .slice(2);
@@ -159,11 +159,3 @@ function lock(lockName, ttl, callback) {
     }
   );
 }
-
-exports.connect = connect;
-exports.disconnect = disconnect;
-exports.get = get;
-exports.set = set;
-exports.del = del;
-exports.pop = pop;
-exports.lock = lock;