IndexedDB in Backbone

As the IndexedDB API is more complex than localStorage, it will be more difficult to create an IndexedDB driver for Backbone as we did with localStorage; in this section, you will use what you have learned about IndexedDB in order to build a driver for Backbone.

The driver should open a database and initialize the stores when it is created for the first time:

// indexedDB/dataStore.js
'use strict';

var Backbone = require('backbone');

const ID_LENGTH = 10;

var contacts = [
  // ...
];

class DataStore {
constructor() {
this.databaseName = 'contacts';
  }

openDatabase() {
var defer = Backbone.$.Deferred();

    // If a database connection is already active use it,
    // otherwise open a new connection
    if (this.db) {
defer.resolve(this.db);
    } else {
      let request = indexedDB.open(this.databaseName, 1);

request.onupgradeneeded = () => {
        let db = request.result;
this.createStores(db);
      };

request.onsuccess = () => {
        // Cache recently...