Merge pull request #8583 from Snuffleupagus/es6-app

ES6-ify the code in `web/app.js` and `web/viewer.js`

web/viewer.js

@@ -16,18 +16,18 @@
 
 'use strict';
 
-var DEFAULT_URL = 'compressed.tracemonkey-pldi-09.pdf';
+let DEFAULT_URL = 'compressed.tracemonkey-pldi-09.pdf';
 
 if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('CHROME')) {
   (function rewriteUrlClosure() {
     // Run this code outside DOMContentLoaded to make sure that the URL
     // is rewritten as soon as possible.
-    var queryString = document.location.search.slice(1);
-    var m = /(^|&)file=([^&]*)/.exec(queryString);
+    let queryString = document.location.search.slice(1);
+    let m = /(^|&)file=([^&]*)/.exec(queryString);
     DEFAULT_URL = m ? decodeURIComponent(m[2]) : '';
 
     // Example: chrome-extension://.../http://example.com/file.pdf
-    var humanReadableUrl = '/' + DEFAULT_URL + location.hash;
+    let humanReadableUrl = '/' + DEFAULT_URL + location.hash;
     history.replaceState(history.state, '', humanReadableUrl);
     if (top === window) {
       chrome.runtime.sendMessage('showPageAction');
@@ -35,7 +35,7 @@ if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('CHROME')) {
   })();
 }
 
-var pdfjsWebApp;
+let pdfjsWebApp;
 if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('PRODUCTION')) {
   pdfjsWebApp = require('./app.js');
 }
@@ -172,14 +172,13 @@ function getViewerConfiguration() {
 }
 
 function webViewerLoad() {
-  var config = getViewerConfiguration();
+  let config = getViewerConfiguration();
   if (typeof PDFJSDev === 'undefined' || !PDFJSDev.test('PRODUCTION')) {
     Promise.all([
       SystemJS.import('pdfjs-web/app'),
       SystemJS.import('pdfjs-web/genericcom'),
       SystemJS.import('pdfjs-web/pdf_print_service'),
-    ]).then(function (modules) {
-      var app = modules[0];
+    ]).then(function([app, ...otherModules]) {
       window.PDFViewerApplication = app.PDFViewerApplication;
       app.PDFViewerApplication.run(config);
     });