Use fat arrow functions `const foo = () => { ... };` for callbacks

and any other function that is passed around and it's not a top level function

28 files changed, 178 insertions, 192 deletions

diff --git a/.eslintrc b/.eslintrc
index ea4d655..b85e51c 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -13,5 +13,10 @@
         "no-var": "error",
         "no-useless-constructor": "error",
         "object-shorthand": ["error", "methods", { "avoidQuotes": true }],
+        "prefer-arrow-callback": "error",
+        "arrow-body-style": ["error", "as-needed", { "requireReturnForObjectLiteral": false } ],
+        "arrow-parens": ["error", "as-needed", { "requireForBlockBody": true }],
+        "arrow-spacing": ["error"],
+        "no-confusing-arrow": ["error", { "allowParens": true }],
     }
 }
diff --git a/app/error-handler.js b/app/error-handler.js
index d813349..96dc926 100644
--- a/app/error-handler.js
+++ b/app/error-handler.js
@@ -2,7 +2,10 @@
 // native support in the browsers, so that our error handler
 // can catch script-loading errors.
 
-(function(){
+// No ES6 can be used in this file since it's used for the translation
+/* eslint-disable prefer-arrow-callback */
+
+(function() {
     "use strict";
 
     // Fallback for all uncought errors
diff --git a/app/ui.js b/app/ui.js
index a8537fb..4fe2a3f 100644
--- a/app/ui.js
+++ b/app/ui.js
@@ -71,7 +71,7 @@ const UI = {
         if (isTouchDevice) {
             document.documentElement.classList.add("noVNC_touch");
             // Remove the address bar
-            setTimeout(function() { window.scrollTo(0, 1); }, 100);
+            setTimeout(() => window.scrollTo(0, 1), 100);
         }
 
         // Restore control bar position
@@ -230,13 +230,13 @@ const UI = {
 
     addTouchSpecificHandlers() {
         document.getElementById("noVNC_mouse_button0")
-            .addEventListener('click', function () { UI.setMouseButton(1); });
+            .addEventListener('click', () => UI.setMouseButton(1));
         document.getElementById("noVNC_mouse_button1")
-            .addEventListener('click', function () { UI.setMouseButton(2); });
+            .addEventListener('click', () => UI.setMouseButton(2));
         document.getElementById("noVNC_mouse_button2")
-            .addEventListener('click', function () { UI.setMouseButton(4); });
+            .addEventListener('click', () => UI.setMouseButton(4));
         document.getElementById("noVNC_mouse_button4")
-            .addEventListener('click', function () { UI.setMouseButton(0); });
+            .addEventListener('click', () => UI.setMouseButton(0));
         document.getElementById("noVNC_keyboard_button")
             .addEventListener('click', UI.toggleVirtualKeyboard);
 
@@ -250,7 +250,7 @@ const UI = {
         document.getElementById("noVNC_keyboardinput")
             .addEventListener('blur', UI.onblurVirtualKeyboard);
         document.getElementById("noVNC_keyboardinput")
-            .addEventListener('submit', function () { return false; });
+            .addEventListener('submit', () => false);
 
         document.documentElement
             .addEventListener('mousedown', UI.keepVirtualKeyboard, true);
@@ -294,11 +294,11 @@ const UI = {
 
     addMachineHandlers() {
         document.getElementById("noVNC_shutdown_button")
-            .addEventListener('click', function() { UI.rfb.machineShutdown(); });
+            .addEventListener('click', () => UI.rfb.machineShutdown());
         document.getElementById("noVNC_reboot_button")
-            .addEventListener('click', function() { UI.rfb.machineReboot(); });
+            .addEventListener('click', () => UI.rfb.machineReboot());
         document.getElementById("noVNC_reset_button")
-            .addEventListener('click', function() { UI.rfb.machineReset(); });
+            .addEventListener('click', () => UI.rfb.machineReset());
         document.getElementById("noVNC_power_button")
             .addEventListener('click', UI.togglePowerPanel);
     },
@@ -329,7 +329,7 @@ const UI = {
     addSettingChangeHandler(name, changeFunc) {
         const settingElem = document.getElementById("noVNC_setting_" + name);
         if (changeFunc === undefined) {
-            changeFunc = function () { UI.saveSetting(name); };
+            changeFunc = () => UI.saveSetting(name);
         }
         settingElem.addEventListener('change', changeFunc);
     },
@@ -552,8 +552,7 @@ const UI = {
         const barDisplayStyle = window.getComputedStyle(bar).display;
         if (barDisplayStyle !== 'none') {
             bar.style.transitionDuration = '0s';
-            bar.addEventListener('transitionend', function () {
-                this.style.transitionDuration = ""; });
+            bar.addEventListener('transitionend', () => bar.style.transitionDuration = '');
         }
 
         const anchor = document.getElementById('noVNC_control_bar_anchor');
@@ -1029,7 +1028,7 @@ const UI = {
         UI.rfb.addEventListener("disconnect", UI.disconnectFinished);
         UI.rfb.addEventListener("credentialsrequired", UI.credentials);
         UI.rfb.addEventListener("securityfailure", UI.securityFailed);
-        UI.rfb.addEventListener("capabilities", function () { UI.updatePowerButton(); });
+        UI.rfb.addEventListener("capabilities", UI.updatePowerButton);
         UI.rfb.addEventListener("clipboard", UI.clipboardReceive);
         UI.rfb.addEventListener("bell", UI.bell);
         UI.rfb.addEventListener("desktopname", UI.updateDesktopName);
@@ -1153,9 +1152,8 @@ const UI = {
         document.getElementById('noVNC_password_dlg')
             .classList.add('noVNC_open');
 
-        setTimeout(function () {
-                document.getElementById('noVNC_password_input').focus();
-            }, 100);
+        setTimeout(() => document
+            .getElementById('noVNC_password_input').focus(), 100);
 
         Log.Warn("Server asked for a password");
         UI.showStatus(_("Password is required"), "warning");
@@ -1624,7 +1622,7 @@ const UI = {
             const promise = document.getElementById('noVNC_bell').play();
             // The standards disagree on the return value here
             if (promise) {
-                promise.catch(function(e) {
+                promise.catch((e) => {
                     if (e.name === "NotAllowedError") {
                         // Ignore when the browser doesn't let us play audio.
                         // It is common that the browsers require audio to be
@@ -1655,12 +1653,12 @@ const UI = {
 const LINGUAS = ["de", "el", "es", "nl", "pl", "sv", "tr", "zh_CN", "zh_TW"];
 l10n.setup(LINGUAS);
 if (l10n.language !== "en" && l10n.dictionary === undefined) {
-    WebUtil.fetchJSON('app/locale/' + l10n.language + '.json', function (translations) {
+    WebUtil.fetchJSON('app/locale/' + l10n.language + '.json', (translations) => {
         l10n.dictionary = translations;
 
         // wait for translations to load before loading the UI
         UI.prime();
-    }, function (err) {
+    }, (err) => {
         Log.Error("Failed to load translations: " + err);
         UI.prime();
     });
diff --git a/app/webutil.js b/app/webutil.js
index 18816d1..33d9292 100644
--- a/app/webutil.js
+++ b/app/webutil.js
@@ -119,7 +119,7 @@ export function initSettings (callback /*, ...callbackArgs */) {
     "use strict";
     const callbackArgs = Array.prototype.slice.call(arguments, 1);
     if (window.chrome && window.chrome.storage) {
-        window.chrome.storage.sync.get(function (cfg) {
+        window.chrome.storage.sync.get((cfg) => {
             settings = cfg;
             if (callback) {
                 callback.apply(this, callbackArgs);
@@ -201,7 +201,7 @@ export function injectParamIfMissing (path, param, value) {
         query = [];
     }
 
-    if (!query.some(function (v) { return v.startsWith(param_eq); })) {
+    if (!query.some(v => v.startsWith(param_eq))) {
         query.push(param_eq + encodeURIComponent(value));
         elem.search = "?" + query.join("&");
     }
@@ -224,7 +224,7 @@ export function fetchJSON(path, resolve, reject) {
     const req = new XMLHttpRequest();
     req.open('GET', path);
 
-    req.onload = function () {
+    req.onload = () => {
         if (req.status === 200) {
             let resObj;
             try {
@@ -238,13 +238,9 @@ export function fetchJSON(path, resolve, reject) {
         }
     };
 
-    req.onerror = function (evt) {
-        reject(new Error("XHR encountered an error while trying to load '" + path + "': " + evt.message));
-    };
+    req.onerror = evt => reject(new Error("XHR encountered an error while trying to load '" + path + "': " + evt.message));
 
-    req.ontimeout = function (evt) {
-        reject(new Error("XHR timed out while trying to load '" + path + "'"));
-    };
+    req.ontimeout = evt => reject(new Error("XHR timed out while trying to load '" + path + "'"));
 
     req.send();
 }
diff --git a/core/input/keyboard.js b/core/input/keyboard.js
index 5b46748..2e7b90a 100644
--- a/core/input/keyboard.js
+++ b/core/input/keyboard.js
@@ -307,7 +307,7 @@ export default class Keyboard {
 
         const target = this._target;
         const downList = this._keyDownList;
-        ['AltLeft', 'AltRight'].forEach(function (code) {
+        ['AltLeft', 'AltRight'].forEach((code) => {
             if (!(code in downList)) {
                 return;
             }
@@ -338,11 +338,10 @@ export default class Keyboard {
             const handler = this._eventHandlers.checkalt;
             ['mousedown', 'mouseup', 'mousemove', 'wheel',
              'touchstart', 'touchend', 'touchmove',
-             'keydown', 'keyup'].forEach(function (type) {
+             'keydown', 'keyup'].forEach(type =>
                 document.addEventListener(type, handler,
                                           { capture: true,
-                                            passive: true });
-             });
+                                            passive: true }));
         }
 
         //Log.Debug("<< Keyboard.grab");
@@ -355,9 +354,7 @@ export default class Keyboard {
             const handler = this._eventHandlers.checkalt;
             ['mousedown', 'mouseup', 'mousemove', 'wheel',
              'touchstart', 'touchend', 'touchmove',
-             'keydown', 'keyup'].forEach(function (type) {
-                document.removeEventListener(type, handler);
-            });
+             'keydown', 'keyup'].forEach(type => document.removeEventListener(type, handler));
         }
 
         this._target.removeEventListener('keydown', this._eventHandlers.keydown);
diff --git a/core/rfb.js b/core/rfb.js
index ed765e8..3433030 100644
--- a/core/rfb.js
+++ b/core/rfb.js
@@ -201,17 +201,17 @@ export default class RFB extends EventTargetMixin {
 
         this._sock = new Websock();
         this._sock.on('message', this._handle_message.bind(this));
-        this._sock.on('open', function () {
+        this._sock.on('open', () => {
             if ((this._rfb_connection_state === 'connecting') &&
                 (this._rfb_init_state === '')) {
                 this._rfb_init_state = 'ProtocolVersion';
                 Log.Debug("Starting VNC handshake");
             } else {
                 this._fail("Unexpected server connection while " +
-                        this._rfb_connection_state);
+                           this._rfb_connection_state);
             }
-        }.bind(this));
-        this._sock.on('close', function (e) {
+        });
+        this._sock.on('close', (e) => {
             Log.Debug("WebSocket on-close event");
             let msg = "";
             if (e.code) {
@@ -236,18 +236,16 @@ export default class RFB extends EventTargetMixin {
                     break;
                 case 'disconnected':
                     this._fail("Unexpected server disconnect " +
-                            "when already disconnected " + msg);
+                               "when already disconnected " + msg);
                     break;
                 default:
                     this._fail("Unexpected server disconnect before connecting " +
-                            msg);
+                               msg);
                     break;
             }
             this._sock.off('close');
-        }.bind(this));
-        this._sock.on('error', function (e) {
-            Log.Warn("WebSocket on-error event");
         });
+        this._sock.on('error', e => Log.Warn("WebSocket on-error event"));
 
         // Slight delay of the actual connection so that the caller has
         // time to set up callbacks
@@ -459,7 +457,7 @@ export default class RFB extends EventTargetMixin {
         const stats = this._encStats;
 
         Log.Info("Encoding stats for this connection:");
-        Object.keys(stats).forEach(function (key) {
+        Object.keys(stats).forEach((key) => {
             const s = stats[key];
             if (s[0] + s[1] > 0) {
                 Log.Info("    " + encodingName(key) + ": " + s[0] + " rects");
@@ -467,10 +465,7 @@ export default class RFB extends EventTargetMixin {
         });
 
         Log.Info("Encoding stats since page load:");
-        Object.keys(stats).forEach(function (key) {
-            const s = stats[key];
-            Log.Info("    " + encodingName(key) + ": " + s[1] + " rects");
-        });
+        Object.keys(stats).forEach(key => Log.Info("    " + encodingName(key) + ": " + stats[key][1] + " rects"));
     }
 
     _focusCanvas(event) {
@@ -489,10 +484,10 @@ export default class RFB extends EventTargetMixin {
     _windowResize(event) {
         // If the window resized then our screen element might have
         // as well. Update the viewport dimensions.
-        window.requestAnimationFrame(function () {
+        window.requestAnimationFrame(() => {
             this._updateClip();
             this._updateScale();
-        }.bind(this));
+        });
 
         if (this._resizeSession) {
             // Request changing the resolution of the remote display to
@@ -640,8 +635,7 @@ export default class RFB extends EventTargetMixin {
 
         this._rfb_connection_state = state;
 
-        const smsg = "New state '" + state + "', was '" + oldstate + "'.";
-        Log.Debug(smsg);
+        Log.Debug("New state '" + state + "', was '" + oldstate + "'.");
 
         if (this._disconnTimer && state !== 'disconnecting') {
             Log.Debug("Clearing disconnect timer");
@@ -664,10 +658,10 @@ export default class RFB extends EventTargetMixin {
             case 'disconnecting':
                 this._disconnect();
 
-                this._disconnTimer = setTimeout(function () {
+                this._disconnTimer = setTimeout(() => {
                     Log.Error("Disconnection timed out.");
                     this._updateConnectionState('disconnected');
-                }.bind(this), DISCONNECT_TIMEOUT * 1000);
+                }, DISCONNECT_TIMEOUT * 1000);
                 break;
 
             case 'disconnected':
@@ -2143,7 +2137,7 @@ RFB.encodingHandlers = {
 
         let resetStreams = 0;
         let streamId = -1;
-        const decompress = function (data, expected) {
+        const decompress = (data, expected) => {
             for (let i = 0; i < 4; i++) {
                 if ((resetStreams >> i) & 1) {
                     this._FBU.zlibs[i].reset();
@@ -2159,9 +2153,9 @@ RFB.encodingHandlers = {
 
             //return uncompressed.data;
             return uncompressed;
-        }.bind(this);
+        };
 
-        const indexedToRGBX2Color = function (data, palette, width, height) {
+        const indexedToRGBX2Color = (data, palette, width, height) => {
             // Convert indexed (palette based) image data to RGB
             // TODO: reduce number of calculations inside loop
             const dest = this._destBuff;
@@ -2220,9 +2214,9 @@ RFB.encodingHandlers = {
             }
 
             return dest;
-        }.bind(this);
+        };
 
-        const indexedToRGBX = function (data, palette, width, height) {
+        const indexedToRGBX = (data, palette, width, height) => {
             // Convert indexed (palette based) image data to RGB
             const dest = this._destBuff;
             const total = width * height * 4;
@@ -2235,14 +2229,14 @@ RFB.encodingHandlers = {
             }
 
             return dest;
-        }.bind(this);
+        };
 
         const rQi = this._sock.get_rQi();
         const rQ = this._sock.rQwhole();
         let cmode, data;
         let cl_header, cl_data;
 
-        const handlePalette = function () {
+        const handlePalette = () => {
             const numColors = rQ[rQi + 2] + 1;
             const paletteSize = numColors * 3;
             this._FBU.bytes += paletteSize;
@@ -2300,9 +2294,9 @@ RFB.encodingHandlers = {
 
 
             return true;
-        }.bind(this);
+        };
 
-        const handleCopy = function () {
+        const handleCopy = () => {
             let raw = false;
             const uncompressedSize = this._FBU.width * this._FBU.height * 3;
             if (uncompressedSize < 12) {
@@ -2340,7 +2334,7 @@ RFB.encodingHandlers = {
             this._display.blitRgbImage(this._FBU.x, this._FBU.y, this._FBU.width, this._FBU.height, data, 0, false);
 
             return true;
-        }.bind(this);
+        };
 
         let ctl = this._sock.rQpeek8();
 
diff --git a/core/util/events.js b/core/util/events.js
index 66527fa..a0eddc7 100644
--- a/core/util/events.js
+++ b/core/util/events.js
@@ -120,7 +120,7 @@ export function releaseCapture () {
 
         // There might be events already queued, so we need to wait for
         // them to flush. E.g. contextmenu in Microsoft Edge
-        window.setTimeout(function(expected) {
+        window.setTimeout((expected) => {
             // Only clear it if it's the expected grab (i.e. no one
             // else has initiated a new grab)
             if (_captureIndex === expected) {
diff --git a/core/util/eventtarget.js b/core/util/eventtarget.js
index 7e56cd5..bb8d6e0 100644
--- a/core/util/eventtarget.js
+++ b/core/util/eventtarget.js
@@ -32,7 +32,7 @@ export default class EventTargetMixin {
       if (!this._listeners || !this._listeners.has(event.type)) {
          return true;
       }
-      this._listeners.get(event.type).forEach(function (callback) {
+      this._listeners.get(event.type).forEach((callback) => {
          callback.call(this, event);
       }, this);
       return !event.defaultPrevented;
diff --git a/core/util/logging.js b/core/util/logging.js
index 5669ad2..1f6a71e 100644
--- a/core/util/logging.js
+++ b/core/util/logging.js
@@ -12,10 +12,10 @@
 
 let _log_level = 'warn';
 
-let Debug = function (msg) {};
-let Info = function (msg) {};
-let Warn = function (msg) {};
-let Error = function (msg) {};
+let Debug = () => {};
+let Info = () => {};
+let Warn = () => {};
+let Error = () => {};
 
 export function init_logging (level) {
     if (typeof level === 'undefined') {
@@ -24,7 +24,7 @@ export function init_logging (level) {
         _log_level = level;
     }
 
-    Debug = Info = Warn = Error = function (msg) {};
+    Debug = Info = Warn = Error = () => {};
 
     if (typeof window.console !== "undefined") {
         /* eslint-disable no-console, no-fallthrough */
diff --git a/core/util/polyfill.js b/core/util/polyfill.js
index c991aa2..1971edf 100644
--- a/core/util/polyfill.js
+++ b/core/util/polyfill.js
@@ -38,8 +38,8 @@ if (typeof Object.assign != 'function') {
 }
 
 /* CustomEvent constructor (taken from MDN) */
-(function () {
-    function CustomEvent ( event, params ) {
+(() => {
+    function CustomEvent (event, params) {
         params = params || { bubbles: false, cancelable: false, detail: undefined };
         const evt = document.createEvent( 'CustomEvent' );
         evt.initCustomEvent( event, params.bubbles, params.cancelable, params.detail );
diff --git a/core/websock.js b/core/websock.js
index ce27c5b..9f09230 100644
--- a/core/websock.js
+++ b/core/websock.js
@@ -164,14 +164,12 @@ export default class Websock {
     }
 
     send_string(str) {
-        this.send(str.split('').map(function (chr) {
-            return chr.charCodeAt(0);
-        }));
+        this.send(str.split('').map(chr => chr.charCodeAt(0)));
     }
 
     // Event Handlers
     off(evt) {
-        this._eventHandlers[evt] = function () {};
+        this._eventHandlers[evt] = () => {};
     }
 
     on(evt, handler) {
@@ -196,7 +194,7 @@ export default class Websock {
         this._websocket.binaryType = 'arraybuffer';
 
         this._websocket.onmessage = this._recv_message.bind(this);
-        this._websocket.onopen = (function () {
+        this._websocket.onopen = () => {
             Log.Debug('>> WebSock.onopen');
             if (this._websocket.protocol) {
                 Log.Info("Server choose sub-protocol: " + this._websocket.protocol);
@@ -204,17 +202,17 @@ export default class Websock {
 
             this._eventHandlers.open();
             Log.Debug("<< WebSock.onopen");
-        }).bind(this);
-        this._websocket.onclose = (function (e) {
+        };
+        this._websocket.onclose = (e) => {
             Log.Debug(">> WebSock.onclose");
             this._eventHandlers.close(e);
             Log.Debug("<< WebSock.onclose");
-        }).bind(this);
-        this._websocket.onerror = (function (e) {
+        };
+        this._websocket.onerror = (e) => {
             Log.Debug(">> WebSock.onerror: " + e);
             this._eventHandlers.error(e);
             Log.Debug("<< WebSock.onerror: " + e);
-        }).bind(this);
+        };
     }
 
     close() {
@@ -225,7 +223,7 @@ export default class Websock {
                 this._websocket.close();
             }
 
-            this._websocket.onmessage = function (e) { return; };
+            this._websocket.onmessage = () => {};
         }
     }
 
diff --git a/karma.conf.js b/karma.conf.js
index 9727c4c..f0a1343 100644
--- a/karma.conf.js
+++ b/karma.conf.js
@@ -1,6 +1,6 @@
 // Karma configuration
 
-module.exports = function(config) {
+module.exports = (config) => {
   const customLaunchers = {};
   let browsers = [];
   let useSauce = false;
diff --git a/po/xgettext-html b/po/xgettext-html
index 87638cb..ddb2cb2 100755
--- a/po/xgettext-html
+++ b/po/xgettext-html
@@ -89,7 +89,7 @@ for (let i = 0; i < opt.argv.length; i++) {
     const dom = new jsdom.JSDOM(file, { includeNodeLocations: true });
     const body = dom.window.document.body;
 
-    const locator = function (elem) {
+    const locator = (elem) => {
         const offset = dom.nodeLocation(elem).startOffset;
         const line = file.slice(0, offset).split("\n").length;
         return fn + ":" + line;
diff --git a/tests/.eslintrc b/tests/.eslintrc
index b52ebaf..dabeb4b 100644
--- a/tests/.eslintrc
+++ b/tests/.eslintrc
@@ -5,5 +5,8 @@
     },
     "globals": {
         "chai": true
+    },
+    "rules": {
+        "prefer-arrow-callback": 0
     }
 }
\ No newline at end of file
diff --git a/tests/assertions.js b/tests/assertions.js
index a336a7a..ba931c2 100644
--- a/tests/assertions.js
+++ b/tests/assertions.js
@@ -32,7 +32,7 @@ chai.use(function (_chai, utils) {
 
     _chai.Assertion.addMethod('sent', function (target_data) {
         const obj = this._obj;
-        obj.inspect = function () {
+        obj.inspect = () => {
             const res = { _websocket: obj._websocket, rQi: obj._rQi, _rQ: new Uint8Array(obj._rQ.buffer, 0, obj._rQlen),
                         _sQ: new Uint8Array(obj._sQ.buffer, 0, obj._sQlen) };
             res.prototype = obj;
diff --git a/tests/fake.websocket.js b/tests/fake.websocket.js
index e0290ed..2e1a3b9 100644
--- a/tests/fake.websocket.js
+++ b/tests/fake.websocket.js
@@ -74,7 +74,7 @@ FakeWebSocket.CLOSED = WebSocket.CLOSED;
 
 FakeWebSocket.__is_fake = true;
 
-FakeWebSocket.replace = function () {
+FakeWebSocket.replace = () => {
     if (!WebSocket.__is_fake) {
         const real_version = WebSocket;
         // eslint-disable-next-line no-global-assign
@@ -83,7 +83,7 @@ FakeWebSocket.replace = function () {
     }
 };
 
-FakeWebSocket.restore = function () {
+FakeWebSocket.restore = () => {
     if (WebSocket.__is_fake) {
         // eslint-disable-next-line no-global-assign
         WebSocket = WebSocket.__real_version;
diff --git a/tests/playback-ui.js b/tests/playback-ui.js
index d2d0869..295f983 100644
--- a/tests/playback-ui.js
+++ b/tests/playback-ui.js
@@ -21,7 +21,7 @@ function loadFile() {
 
     message("Loading " + fname);
 
-    return new Promise(function (resolve, reject) {
+    return new Promise((resolve, reject) => {
         const script = document.createElement("script");
         script.onload = resolve;
         script.onerror = reject;
@@ -67,9 +67,9 @@ class IterationPlayer {
 
         this._state = 'running';
 
-    this.onfinish = function() {};
-    this.oniterationfinish = function() {};
-    this.rfbdisconnected = function() {};
+        this.onfinish = () => {};
+        this.oniterationfinish = () => {};
+        this.rfbdisconnected = () => {};
     }
 
     start(mode) {
@@ -147,15 +147,15 @@ function start() {
     }
 
     const player = new IterationPlayer(iterations, frames, encoding);
-    player.oniterationfinish = function (evt) {
+    player.oniterationfinish = (evt) => {
         message(`Iteration ${evt.number} took ${evt.duration}ms`);
     };
-    player.onrfbdisconnected = function (evt) {
+    player.onrfbdisconnected = (evt) => {
         if (!evt.clean) {
             message(`noVNC sent disconnected during iteration ${evt.iteration} frame ${evt.frame}`);
         }
     };
-    player.onfinish = function (evt) {
+    player.onfinish = (evt) => {
         const iterTime = parseInt(evt.duration / evt.iterations, 10);
         message(`${evt.iterations} iterations took ${evt.duration}ms (average ${iterTime}ms / iteration)`);
 
@@ -165,4 +165,4 @@ function start() {
     player.start(mode);
 }
 
-loadFile().then(enableUI).catch(function (e) { message("Error loading recording: " + e); });
+loadFile().then(enableUI).catch(e => message("Error loading recording: " + e));
diff --git a/tests/playback.js b/tests/playback.js
index 6b422d8..cac9c8a 100644
--- a/tests/playback.js
+++ b/tests/playback.js
@@ -13,18 +13,18 @@ if (window.setImmediate === undefined) {
     let _immediateIdCounter = 1;
     const _immediateFuncs = {};
 
-    window.setImmediate = function (func) {
+    window.setImmediate = (func) => {
         const index = _immediateIdCounter++;
         _immediateFuncs[index] = func;
         window.postMessage("noVNC immediate trigger:" + index, "*");
         return index;
     };
 
-    window.clearImmediate = function (id) {
+    window.clearImmediate = (id) => {
         _immediateFuncs[id];
     };
 
-    const _onMessage = function (event) {
+    const _onMessage = (event) => {
         if ((typeof event.data !== "string") ||
             (event.data.indexOf("noVNC immediate trigger:") !== 0)) {
             return;
@@ -71,7 +71,7 @@ export default class RecordingPlayer {
 
         this._running = false;
 
-    this.onfinish = function () {};
+        this.onfinish = () => {};
     }
 
     run(realtime, trafficManagement) {
@@ -96,9 +96,9 @@ export default class RecordingPlayer {
 
     // _enablePlaybackMode mocks out things not required for running playback
     _enablePlaybackMode() {
-        this._rfb._sock.send = function (arr) {};
-        this._rfb._sock.close = function () {};
-        this._rfb._sock.flush = function () {};
+        this._rfb._sock.send = () => {};
+        this._rfb._sock.close = () => {};
+        this._rfb._sock.flush = () => {};
         this._rfb._sock.open = function () {
             this.init();
             this._eventHandlers.open();
@@ -143,12 +143,11 @@ export default class RecordingPlayer {
     _doPacket() {
         // Avoid having excessive queue buildup in non-realtime mode
         if (this._trafficManagement && this._rfb._flushing) {
-            const player = this;
             const orig = this._rfb._display.onflush;
-            this._rfb._display.onflush = function () {
-                player._rfb._display.onflush = orig;
-                player._rfb._onFlush();
-                player._doPacket();
+            this._rfb._display.onflush = () => {
+                this._rfb._display.onflush = orig;
+                this._rfb._onFlush();
+                this._doPacket();
             };
             return;
         }
@@ -174,12 +173,11 @@ export default class RecordingPlayer {
 
     _finish() {
         if (this._rfb._display.pending()) {
-            const player = this;
-            this._rfb._display.onflush = function () {
-                if (player._rfb._flushing) {
-                    player._rfb._onFlush();
+            this._rfb._display.onflush = () => {
+                if (this._rfb._flushing) {
+                    this._rfb._onFlush();
                 }
-                player._finish();
+                this._finish();
             };
             this._rfb._display.flush();
         } else {
diff --git a/tests/test.base64.js b/tests/test.base64.js
index 0ff4bfe..a972448 100644
--- a/tests/test.base64.js
+++ b/tests/test.base64.js
@@ -27,7 +27,7 @@ describe('Base64 Tools', function() {
         });
 
         it('should throw an error if we have extra characters at the end of the string', function() {
-            expect(function () { Base64.decode(B64_STR+'abcdef'); }).to.throw(Error);
+            expect(() => Base64.decode(B64_STR+'abcdef')).to.throw(Error);
         });
     });
 });
diff --git a/tests/test.display.js b/tests/test.display.js
index a7afd06..e3810ef 100644
--- a/tests/test.display.js
+++ b/tests/test.display.js
@@ -284,7 +284,7 @@ describe('Display/Canvas Helper', function () {
         it('should draw the logo on #clear with a logo set', function (done) {
             display._logo = { width: 4, height: 4, type: "image/png", data: make_image_png(checked_data) };
             display.clear();
-            display.onflush = function () {
+            display.onflush = () => {
                 expect(display).to.have.displayed(checked_data);
                 expect(display._fb_width).to.equal(4);
                 expect(display._fb_height).to.equal(4);
@@ -325,7 +325,7 @@ describe('Display/Canvas Helper', function () {
         it('should support drawing images via #imageRect', function (done) {
             display.imageRect(0, 0, "image/png", make_image_png(checked_data));
             display.flip();
-            display.onflush = function () {
+            display.onflush = () => {
                 expect(display).to.have.displayed(checked_data);
                 done();
             };
diff --git a/tests/test.keyboard.js b/tests/test.keyboard.js
index 3d409fb..c555b4f 100644
--- a/tests/test.keyboard.js
+++ b/tests/test.keyboard.js
@@ -24,7 +24,7 @@ describe('Key Event Handling', function() {
         it('should decode keydown events', function(done) {
             if (browser.isIE() || browser.isEdge()) this.skip();
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0x61);
                 expect(code).to.be.equal('KeyA');
                 expect(down).to.be.equal(true);
@@ -36,7 +36,7 @@ describe('Key Event Handling', function() {
             if (browser.isIE() || browser.isEdge()) this.skip();
             let calls = 0;
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0x61);
                 expect(code).to.be.equal('KeyA');
                 if (calls++ === 1) {
@@ -57,7 +57,7 @@ describe('Key Event Handling', function() {
             });
             it('should decode keypress events', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('KeyA');
                     expect(down).to.be.equal(true);
@@ -75,7 +75,7 @@ describe('Key Event Handling', function() {
             });
             it('should handle keypress with missing code', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('KeyA');
                     expect(down).to.be.equal(true);
@@ -86,7 +86,7 @@ describe('Key Event Handling', function() {
             });
             it('should guess key if no keypress and numeric key', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x32);
                     expect(code).to.be.equal('Digit2');
                     expect(down).to.be.equal(true);
@@ -96,7 +96,7 @@ describe('Key Event Handling', function() {
             });
             it('should guess key if no keypress and alpha key', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('KeyA');
                     expect(down).to.be.equal(true);
@@ -106,7 +106,7 @@ describe('Key Event Handling', function() {
             });
             it('should guess key if no keypress and alpha key (with shift)', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x41);
                     expect(code).to.be.equal('KeyA');
                     expect(down).to.be.equal(true);
@@ -116,7 +116,7 @@ describe('Key Event Handling', function() {
             });
             it('should not guess key if no keypress and unknown key', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0);
                     expect(code).to.be.equal('KeyA');
                     expect(down).to.be.equal(true);
@@ -161,7 +161,7 @@ describe('Key Event Handling', function() {
             if (browser.isIE() || browser.isEdge()) this.skip();
             let count = 0;
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 switch (count++) {
                     case 0:
                         expect(keysym).to.be.equal(0x61);
@@ -208,7 +208,7 @@ describe('Key Event Handling', function() {
                 if (browser.isIE() || browser.isEdge()) this.skip();
                 let count = 0;
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     switch (count++) {
                         case 0:
                             expect(keysym).to.be.equal(0x61);
@@ -233,7 +233,7 @@ describe('Key Event Handling', function() {
         });
         it('should send release using the same keysym as the press', function(done) {
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0x61);
                 expect(code).to.be.equal('KeyA');
                 if (!down) {
@@ -246,7 +246,7 @@ describe('Key Event Handling', function() {
         it('should send the same keysym for multiple presses', function() {
             let count = 0;
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0x61);
                 expect(code).to.be.equal('KeyA');
                 expect(down).to.be.equal(true);
@@ -266,7 +266,7 @@ describe('Key Event Handling', function() {
         describe('Legacy Events', function() {
             it('should track keys using keyCode if no code', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('Platform65');
                     if (!down) {
@@ -278,7 +278,7 @@ describe('Key Event Handling', function() {
             });
             it('should ignore compositing code', function() {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('Unidentified');
                 };
@@ -286,7 +286,7 @@ describe('Key Event Handling', function() {
             });
             it('should track keys using keyIdentifier if no code', function(done) {
                 const kbd = new Keyboard(document);
-                kbd.onkeyevent = function(keysym, code, down) {
+                kbd.onkeyevent = (keysym, code, down) => {
                     expect(keysym).to.be.equal(0x61);
                     expect(code).to.be.equal('Platform65');
                     if (!down) {
@@ -328,7 +328,7 @@ describe('Key Event Handling', function() {
         it('should change Alt to AltGraph', function() {
             let count = 0;
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 switch (count++) {
                     case 0:
                         expect(keysym).to.be.equal(0xFF7E);
@@ -346,7 +346,7 @@ describe('Key Event Handling', function() {
         });
         it('should change left Super to Alt', function(done) {
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0xFFE9);
                 expect(code).to.be.equal('MetaLeft');
                 done();
@@ -355,7 +355,7 @@ describe('Key Event Handling', function() {
         });
         it('should change right Super to left Super', function(done) {
             const kbd = new Keyboard(document);
-            kbd.onkeyevent = function(keysym, code, down) {
+            kbd.onkeyevent = (keysym, code, down) => {
                 expect(keysym).to.be.equal(0xFFEB);
                 expect(code).to.be.equal('MetaRight');
                 done();
diff --git a/tests/test.mouse.js b/tests/test.mouse.js
index 58200a4..61db064 100644
--- a/tests/test.mouse.js
+++ b/tests/test.mouse.js
@@ -18,7 +18,7 @@ describe('Mouse Event Handling', function() {
 
     // The real constructors might not work everywhere we
     // want to run these tests
-    const mouseevent = function(typeArg, MouseEventInit) {
+    const mouseevent = (typeArg, MouseEventInit) => {
         const e = { type: typeArg };
         for (let key in MouseEventInit) {
             e[key] = MouseEventInit[key];
@@ -32,7 +32,7 @@ describe('Mouse Event Handling', function() {
     describe('Decode Mouse Events', function() {
         it('should decode mousedown events', function(done) {
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 expect(bmask).to.be.equal(0x01);
                 expect(down).to.be.equal(1);
                 done();
@@ -42,7 +42,7 @@ describe('Mouse Event Handling', function() {
         it('should decode mouseup events', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 expect(bmask).to.be.equal(0x01);
                 if (calls++ === 1) {
                     expect(down).to.not.be.equal(1);
@@ -54,7 +54,7 @@ describe('Mouse Event Handling', function() {
         });
         it('should decode mousemove events', function(done) {
             const mouse = new Mouse(target);
-            mouse.onmousemove = function(x, y) {
+            mouse.onmousemove = (x, y) => {
                 // Note that target relative coordinates are sent
                 expect(x).to.be.equal(40);
                 expect(y).to.be.equal(10);
@@ -66,7 +66,7 @@ describe('Mouse Event Handling', function() {
         it('should decode mousewheel events', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 calls++;
                 expect(bmask).to.be.equal(1<<6);
                 if (calls === 1) {
@@ -90,7 +90,7 @@ describe('Mouse Event Handling', function() {
         it('should use same pos for 2nd tap if close enough', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 calls++;
                 if (calls === 1) {
                     expect(down).to.be.equal(1);
@@ -121,7 +121,7 @@ describe('Mouse Event Handling', function() {
         it('should not modify 2nd tap pos if far apart', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 calls++;
                 if (calls === 1) {
                     expect(down).to.be.equal(1);
@@ -150,7 +150,7 @@ describe('Mouse Event Handling', function() {
         it('should not modify 2nd tap pos if not soon enough', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 calls++;
                 if (calls === 1) {
                     expect(down).to.be.equal(1);
@@ -179,7 +179,7 @@ describe('Mouse Event Handling', function() {
         it('should not modify 2nd tap pos if not touch', function(done) {
             let calls = 0;
             const mouse = new Mouse(target);
-            mouse.onmousebutton = function(x, y, down, bmask) {
+            mouse.onmousebutton = (x, y, down, bmask) => {
                 calls++;
                 if (calls === 1) {
                     expect(down).to.be.equal(1);
diff --git a/tests/test.rfb.js b/tests/test.rfb.js
index cb72f4c..3d5bd28 100644
--- a/tests/test.rfb.js
+++ b/tests/test.rfb.js
@@ -8,7 +8,7 @@ import FakeWebSocket from './fake.websocket.js';
 import sinon from '../vendor/sinon.js';
 
 /* UIEvent constructor polyfill for IE */
-(function () {
+(() => {
     if (typeof window.UIEvent === "function") return;
 
     function UIEvent ( event, params ) {
@@ -23,18 +23,18 @@ import sinon from '../vendor/sinon.js';
     window.UIEvent = UIEvent;
 })();
 
-const push8 = function (arr, num) {
+const push8 = (arr, num) => {
     "use strict";
     arr.push(num & 0xFF);
 };
 
-const push16 = function (arr, num) {
+const push16 = (arr, num) => {
     "use strict";
     arr.push((num >> 8) & 0xFF,
               num & 0xFF);
 };
 
-const push32 = function (arr, num) {
+const push32 = (arr, num) => {
     "use strict";
     arr.push((num >> 24) & 0xFF,
               (num >> 16) & 0xFF,
@@ -852,7 +852,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
             it('should not result in a connect event if the state is not "connected"', function () {
                 const spy = sinon.spy();
                 client.addEventListener("connect", spy);
-                client._sock._websocket.open = function () {};  // explicitly don't call onopen
+                client._sock._websocket.open = () => {};  // explicitly don't call onopen
                 client._updateConnectionState('connecting');
                 expect(spy).to.not.have.been.called;
             });
@@ -866,7 +866,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
 
             it('should force disconnect if we do not call Websock.onclose within the disconnection timeout', function () {
                 sinon.spy(client, '_updateConnectionState');
-                client._sock._websocket.close = function () {};  // explicitly don't call onclose
+                client._sock._websocket.close = () => {};  // explicitly don't call onclose
                 client._updateConnectionState('disconnecting');
                 this.clock.tick(3 * 1000);
                 expect(client._updateConnectionState).to.have.been.calledTwice;
@@ -891,7 +891,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
             it('should not result in a disconnect event', function () {
                 const spy = sinon.spy();
                 client.addEventListener("disconnect", spy);
-                client._sock._websocket.close = function () {};  // explicitly don't call onclose
+                client._sock._websocket.close = () => {};  // explicitly don't call onclose
                 client._updateConnectionState('disconnecting');
                 expect(spy).to.not.have.been.called;
             });
@@ -1239,11 +1239,10 @@ describe('Remote Frame Buffer Protocol Client', function() {
                 });
 
                 function send_num_str_pairs(pairs, client) {
-                    const pairs_len = pairs.length;
                     const data = [];
-                    push32(data, pairs_len);
+                    push32(data, pairs.length);
 
-                    for (let i = 0; i < pairs_len; i++) {
+                    for (let i = 0; i < pairs.length; i++) {
                         push32(data, pairs[i][0]);
                         for (let j = 0; j < 4; j++) {
                             data.push(pairs[i][1].charCodeAt(j));
@@ -1618,7 +1617,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
                 const expected_msg = {_sQ: new Uint8Array(10), _sQlen: 0, flush: () => {}};
                 RFB.messages.fbUpdateRequest(expected_msg, true, 0, 0, 640, 20);
 
-                client._framebufferUpdate = function () { return true; };
+                client._framebufferUpdate = () => true;
                 client._sock._websocket._receive_data(new Uint8Array([0]));
 
                 expect(client._sock).to.have.sent(expected_msg._sQ);
@@ -1645,7 +1644,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
 
             it('should not send a request in continuous updates mode', function () {
                 client._enabledContinuousUpdates = true;
-                client._framebufferUpdate = function () { return true; };
+                client._framebufferUpdate = () => true;
                 client._sock._websocket._receive_data(new Uint8Array([0]));
 
                 expect(client._sock._websocket._get_sent_data()).to.have.length(0);
@@ -2231,7 +2230,7 @@ describe('Remote Frame Buffer Protocol Client', function() {
             // close events
             it('should transition to "disconnected" from "disconnecting" on a close event', function () {
                 const real = client._sock._websocket.close;
-                client._sock._websocket.close = function () {};
+                client._sock._websocket.close = () => {};
                 client.disconnect();
                 expect(client._rfb_connection_state).to.equal('disconnecting');
                 client._sock._websocket.close = real;
diff --git a/tests/test.websock.js b/tests/test.websock.js
index eb46df5..124d1bf 100644
--- a/tests/test.websock.js
+++ b/tests/test.websock.js
@@ -178,7 +178,7 @@ describe('Websock', function() {
 
             it('should raise an error if we try to go back more than possible', function () {
                 sock.set_rQi(5);
-                expect(function () { sock.rQwait('hi', RQ_TEMPLATE.length, 6); }).to.throw(Error);
+                expect(() => sock.rQwait('hi', RQ_TEMPLATE.length, 6)).to.throw(Error);
             });
 
             it('should not reduce rQi if there are enough bytes', function () {
diff --git a/utils/genkeysymdef.js b/utils/genkeysymdef.js
index 9d09775..cd89a68 100755
--- a/utils/genkeysymdef.js
+++ b/utils/genkeysymdef.js
@@ -108,7 +108,7 @@ out +=
 "};\n" +
 "\n" +
 "export default {\n" +
-"    lookup : function(u) {\n" +
+"    lookup(u) {\n" +
 "        // Latin-1 is one-to-one mapping\n" +
 "        if ((u >= 0x20) && (u <= 0xff)) {\n" +
 "            return u;\n" +
diff --git a/utils/use_require.js b/utils/use_require.js
index 2d45f61..0dbdb0a 100755
--- a/utils/use_require.js
+++ b/utils/use_require.js
@@ -39,15 +39,14 @@ const no_transform_files = new Set([
     path.join(paths.app, 'error-handler.js'),
 ]);
 
-no_copy_files.forEach((file) => no_transform_files.add(file));
+no_copy_files.forEach(file => no_transform_files.add(file));
 
 // util.promisify requires Node.js 8.x, so we have our own
 function promisify(original) {
     return function () {
-        const obj = this;
         const args = Array.prototype.slice.call(arguments);
         return new Promise((resolve, reject) => {
-            original.apply(obj, args.concat((err, value) => {
+            original.apply(this, args.concat((err, value) => {
                 if (err) return reject(err);
                 resolve(value);
             }));
@@ -70,29 +69,27 @@ const babelTransformFile = promisify(babel.transformFile);
 
 // walkDir *recursively* walks directories trees,
 // calling the callback for all normal files found.
-const walkDir = function (base_path, cb, filter) {
+function walkDir(base_path, cb, filter) {
     return readdir(base_path)
-    .then(files => {
+    .then((files) => {
         const paths = files.map(filename => path.join(base_path, filename));
-        return Promise.all(paths.map((filepath) => {
-            return lstat(filepath)
-            .then(stats => {
-                if (filter !== undefined && !filter(filepath, stats)) return;
-
-                if (stats.isSymbolicLink()) return;
-                if (stats.isFile()) return cb(filepath);
-                if (stats.isDirectory()) return walkDir(filepath, cb, filter);
-            });
-        }));
+        return Promise.all(paths.map(filepath => lstat(filepath)
+        .then((stats) => {
+            if (filter !== undefined && !filter(filepath, stats)) return;
+
+            if (stats.isSymbolicLink()) return;
+            if (stats.isFile()) return cb(filepath);
+            if (stats.isDirectory()) return walkDir(filepath, cb, filter);
+        })));
     });
-};
+}
 
-const transform_html = function (legacy_scripts, only_legacy) {
+function transform_html (legacy_scripts, only_legacy) {
     // write out the modified vnc.html file that works with the bundle
     const src_html_path = path.resolve(__dirname, '..', 'vnc.html');
     const out_html_path = path.resolve(paths.out_dir_base, 'vnc.html');
     return readFile(src_html_path)
-    .then(contents_raw => {
+    .then((contents_raw) => {
         let contents = contents_raw.toString();
 
         const start_marker = '<!-- begin scripts -->\n';
@@ -141,7 +138,7 @@ const transform_html = function (legacy_scripts, only_legacy) {
     });
 }
 
-const make_lib_files = function (import_format, source_maps, with_app_dir, only_legacy) {
+function make_lib_files(import_format, source_maps, with_app_dir, only_legacy) {
     if (!import_format) {
         throw new Error("you must specify an import format to generate compiled noVNC libraries");
     } else if (!SUPPORTED_FORMATS.has(import_format)) {
@@ -223,7 +220,7 @@ const make_lib_files = function (import_format, source_maps, with_app_dir, only_
             }
 
             return babelTransformFile(filename, opts)
-            .then(res => {
+            .then((res) => {
                 console.log(`Writing ${legacy_path}`);
                 const {map} = res;
                 let {code} = res;
@@ -275,7 +272,7 @@ const make_lib_files = function (import_format, source_maps, with_app_dir, only_
         const out_app_path = path.join(legacy_path_base, 'app.js');
         console.log(`Writing ${out_app_path}`);
         return helper.appWriter(out_path_base, legacy_path_base, out_app_path)
-        .then(extra_scripts => {
+        .then((extra_scripts) => {
             const rel_app_path = path.relative(out_path_base, out_app_path);
             const legacy_scripts = extra_scripts.concat([rel_app_path]);
             transform_html(legacy_scripts, only_legacy);
@@ -283,18 +280,17 @@ const make_lib_files = function (import_format, source_maps, with_app_dir, only_
         .then(() => {
             if (!helper.removeModules) return;
             console.log(`Cleaning up temporary files...`);
-            return Promise.all(outFiles.map(filepath => {
+            return Promise.all(outFiles.map((filepath) => {
                 unlink(filepath)
                 .then(() => {
                     // Try to clean up any empty directories if this
                     // was the last file in there
-                    const rmdir_r = dir => {
-                        return rmdir(dir)
+                    const rmdir_r = dir =>
+                        rmdir(dir)
                         .then(() => rmdir_r(path.dirname(dir)))
                         .catch(() => {
                             // Assume the error was ENOTEMPTY and ignore it
                         });
-                    };
                     return rmdir_r(path.dirname(filepath));
                 });
             }));
@@ -304,7 +300,7 @@ const make_lib_files = function (import_format, source_maps, with_app_dir, only_
         console.error(`Failure converting modules: ${err}`);
         process.exit(1);
     });
-};
+}
 
 if (program.clean) {
     console.log(`Removing ${paths.lib_dir_base}`);
diff --git a/utils/use_require_helpers.js b/utils/use_require_helpers.js
index 532e8f1..f0cbcf5 100644
--- a/utils/use_require_helpers.js
+++ b/utils/use_require_helpers.js
@@ -5,10 +5,9 @@ const path = require('path');
 // util.promisify requires Node.js 8.x, so we have our own
 function promisify(original) {
     return function () {
-        const obj = this;
         const args = Array.prototype.slice.call(arguments);
         return new Promise((resolve, reject) => {
-            original.apply(obj, args.concat((err, value) => {
+            original.apply(this, args.concat((err, value) => {
                 if (err) return reject(err);
                 resolve(value);
             }));
@@ -24,7 +23,7 @@ module.exports = {
             // setup for requirejs
             const ui_path = path.relative(base_out_path,
                                         path.join(script_base_path, 'app', 'ui'));
-            return writeFile(out_path, `requirejs(["${ui_path}"], function (ui) {});`)
+            return writeFile(out_path, `requirejs(["${ui_path}"], (ui) => {});`)
             .then(() => {
                 console.log(`Please place RequireJS in ${path.join(script_base_path, 'require.js')}`);
                 const require_path = path.relative(base_out_path,
@@ -43,7 +42,7 @@ module.exports = {
             const browserify = require('browserify');
             const b = browserify(path.join(script_base_path, 'app/ui.js'), {});
             return promisify(b.bundle).call(b)
-            .then((buf) => writeFile(out_path, buf))
+            .then(buf => writeFile(out_path, buf))
             .then(() => []);
         },
         noCopyOverride: () => {},
diff --git a/vnc_lite.html b/vnc_lite.html
index 4a96d44..c580e11 100644
--- a/vnc_lite.html
+++ b/vnc_lite.html
@@ -229,7 +229,7 @@
             rfb.viewOnly = WebUtil.getConfigVar('view_only', false);
             rfb.addEventListener("connect",  connected);
             rfb.addEventListener("disconnect", disconnected);
-            rfb.addEventListener("capabilities", function () { updatePowerButtons(); });
+            rfb.addEventListener("capabilities", updatePowerButtons);
             rfb.addEventListener("credentialsrequired", credentials);
             rfb.addEventListener("desktopname", updateDesktopName);
             rfb.scaleViewport = WebUtil.getConfigVar('scale', false);