Simplify the source code

Simplify the source code by using some ES6 features such as arrow
functions to avoid the use of 'var self = this', the shorthand for
method definitions in object initializers.

modules/RTC/ScreenObtainer.js

 /* global chrome, $, alert */
 
+var AdapterJS = require("./adapter.screenshare");
+var GlobalOnErrorHandler = require("../util/GlobalOnErrorHandler");
 var logger = require("jitsi-meet-logger").getLogger(__filename);
 var RTCBrowserType = require("./RTCBrowserType");
-var AdapterJS = require("./adapter.screenshare");
 import JitsiTrackError from "../../JitsiTrackError";
 import * as JitsiTrackErrors from "../../JitsiTrackErrors";
-var GlobalOnErrorHandler = require("../util/GlobalOnErrorHandler");
 
 /**
  * Indicates whether the Chrome desktop sharing extension is installed.
  */
 var ScreenObtainer = {
     obtainStream: null,
+
     /**
      * Initializes the function used to obtain a screen capture
      * (this.obtainStream).
      * @param options {object}
      * @param gum {Function} GUM method
      */
-    init: function(options, gum) {
+    init(options, gum) {
         var obtainDesktopStream = null;
         this.options = options = options || {};
         GUM = gum;
             (options.desktopSharingChromeMethod || options.desktopSharing);
 
         if (RTCBrowserType.isNWJS()) {
-            obtainDesktopStream = function (options, onSuccess, onFailure) {
+            obtainDesktopStream = (options, onSuccess, onFailure) => {
                 window.JitsiMeetNW.obtainDesktopStream (
-                    onSuccess, function (error, constraints) {
+                    onSuccess,
+                    (error, constraints) => {
                         var jitsiError;
                         // FIXME:
                         // This is very very durty fix for recognising that the
             } else {
                 obtainDesktopStream = this.obtainScreenOnFirefox;
             }
-
         }
 
         if (!obtainDesktopStream) {
      * environment.
      * @returns {boolean}
      */
-    isSupported: function() {
+    isSupported() {
         return !!this.obtainStream;
     },
+
     /**
      * Obtains a screen capture stream on Firefox.
      * @param callback
      * @param errorCallback
      */
-    obtainScreenOnFirefox:
-           function (options, callback, errorCallback) {
-        var self = this;
+    obtainScreenOnFirefox(options, callback, errorCallback) {
         var extensionRequired = false;
         if (this.options.desktopSharingFirefoxMaxVersionExtRequired === -1 ||
             (this.options.desktopSharingFirefoxMaxVersionExtRequired >= 0 &&
         // extension if it hasn't.
         if (firefoxExtInstalled === null) {
             window.setTimeout(
-                function() {
+                () => {
                     if (firefoxExtInstalled === null)
                         firefoxExtInstalled = false;
-                    self.obtainScreenOnFirefox(callback, errorCallback);
+                    this.obtainScreenOnFirefox(callback, errorCallback);
                 },
-                300
-            );
+                300);
             logger.log("Waiting for detection of jidesha on firefox to " +
                 "finish.");
             return;
         errorCallback(
             new JitsiTrackError(JitsiTrackErrors.FIREFOX_EXTENSION_NEEDED));
     },
+
     /**
      * Asks Chrome extension to call chooseDesktopMedia and gets chrome
      * 'desktop' stream for returned stream token.
      */
-    obtainScreenFromExtension: function(options, streamCallback, failCallback) {
+    obtainScreenFromExtension(options, streamCallback, failCallback) {
         if (chromeExtInstalled) {
             doGetStreamFromExtension(this.options, streamCallback,
                 failCallback);
             try {
                 chrome.webstore.install(
                     getWebStoreInstallUrl(this.options),
-                    (arg) => {
+                    arg => {
                         logger.log("Extension installed successfully", arg);
                         chromeExtInstalled = true;
-                        // We need to give a moment for the endpoint to become
-                        // available
+                        // We need to give a moment to the endpoint to become
+                        // available.
                         waitForExtensionAfterInstall(this.options, 200, 10)
                             .then(() => {
                                 doGetStreamFromExtension(this.options,
                                     streamCallback, failCallback);
-                            }).catch(() => {
-                                // options param is {} because we won't do
-                                // external install in this case.
-                                this.handleExtensionInstallationError({},
-                                    streamCallback, failCallback);
+                            }).catch(reason => {
+                                this.handleExtensionInstallationError(options,
+                                    streamCallback, failCallback, reason);
                             });
                     },
                     this.handleExtensionInstallationError.bind(this,
             }
         }
     },
-    handleExtensionInstallationError: function (options, streamCallback,
-        failCallback, e) {
-        if( CHROME_EXTENSION_POPUP_ERROR === e && options.interval > 0 &&
-            typeof(options.checkAgain) === "function" &&
-            typeof(options.listener) === "function") {
-            options.listener("waitingForExtension",
-                getWebStoreInstallUrl(this.options));
-            this.checkForChromeExtensionOnInterval(options,
-                streamCallback, failCallback, e);
+
+    handleExtensionInstallationError(options, streamCallback, failCallback, e) {
+        const webStoreInstallUrl = getWebStoreInstallUrl(this.options);
+
+        if (CHROME_EXTENSION_POPUP_ERROR === e
+                && options.interval > 0
+                && typeof(options.checkAgain) === "function"
+                && typeof(options.listener) === "function") {
+            options.listener("waitingForExtension", webStoreInstallUrl);
+            this.checkForChromeExtensionOnInterval(options, streamCallback,
+                failCallback, e);
             return;
         }
-        var msg = "Failed to install the extension from "
-            + getWebStoreInstallUrl(this.options);
 
-        logger.log(msg, e);
+        const msg
+            = "Failed to install the extension from " + webStoreInstallUrl;
 
+        logger.log(msg, e);
         failCallback(new JitsiTrackError(
             JitsiTrackErrors.CHROME_EXTENSION_INSTALLATION_ERROR,
-            msg
-        ));
+            msg));
     },
-    checkForChromeExtensionOnInterval: function (options,
-        streamCallback, failCallback) {
+
+    checkForChromeExtensionOnInterval(options, streamCallback, failCallback) {
         if (options.checkAgain() === false) {
             failCallback(new JitsiTrackError(
                 JitsiTrackErrors.CHROME_EXTENSION_INSTALLATION_ERROR));
     }
 };
 
-
-
 /**
  * Obtains a desktop stream using getUserMedia.
  * For this to work on Chrome, the
  * 'about:config'.
  */
 function obtainWebRTCScreen(options, streamCallback, failCallback) {
-    GUM(
-        ['screen'],
-        streamCallback,
-        failCallback
-    );
+    GUM(['screen'], streamCallback, failCallback);
 }
 
 /**
         //TODO: remove chromeExtensionId (deprecated)
         (options.desktopSharingChromeExtId || options.chromeExtensionId),
         { getVersion: true },
-        function (response) {
+        response => {
             if (!response || !response.version) {
                 // Communication failure - assume that no endpoint exists
                 logger.warn(
             sources: (options.desktopSharingChromeSources ||
                 options.desktopSharingSources)
         },
-        function (response) {
+        response => {
             if (!response) {
                 // possibly re-wraping error message to make code consistent
                 var lastError = chrome.runtime.lastError;
             if (response.streamId) {
                 GUM(
                     ['desktop'],
-                    function (stream) {
-                        streamCallback(stream);
-                    },
+                    stream => streamCallback(stream),
                     failCallback,
-                    {desktopStream: response.streamId});
+                    { desktopStream: response.streamId });
             } else {
                 // As noted in Chrome Desktop Capture API:
                 // If user didn't select any source (i.e. canceled the prompt)
     // Initialize Chrome extension inline installs
     initInlineInstalls(options);
     // Check if extension is installed
-    checkChromeExtInstalled(function (installed, updateRequired) {
+    checkChromeExtInstalled((installed, updateRequired) => {
         chromeExtInstalled = installed;
         chromeExtUpdateRequired = updateRequired;
         logger.info(
     }
 
     var img = document.createElement('img');
-    img.onload = function(){
+    img.onload = () => {
         logger.log("Detected firefox screen sharing extension.");
         firefoxExtInstalled = true;
     };
-    img.onerror = function(){
+    img.onerror = () => {
         logger.log("Detected lack of firefox screen sharing extension.");
         firefoxExtInstalled = false;
     };