Change let into const (puppeteer#457)

This patch:
- changes `let` into `const` throughout codebase
- adds eslint check to prefer const over let

.eslintrc.js

@@ -47,6 +47,7 @@ module.exports = {
         "new-parens": 2,
         "func-call-spacing": 2,
         "arrow-parens": [2, "as-needed"],
+        "prefer-const": 2,
 
         // anti-patterns
         "no-var": 2,

DeviceDescriptors.js

@@ -628,5 +628,5 @@ module.exports = [
     }
   }
 ];
-for (let device of module.exports)
+for (const device of module.exports)
   module.exports[device.name] = device;

install.js

@@ -24,7 +24,7 @@ const revisionInfo = Downloader.revisionInfo(platform, revision);
 if (revisionInfo.downloaded)
   return;
 
-let allRevisions = Downloader.downloadedRevisions();
+const allRevisions = Downloader.downloadedRevisions();
 Downloader.downloadRevision(platform, revision, onProgress)
     // Remove previous chromium revisions.
     .then(() => Promise.all(allRevisions.map(({platform, revision}) => Downloader.removeRevision(platform, revision))))
@@ -52,7 +52,7 @@ function onProgress(bytesTotal, delta) {
 }
 
 function toMegabytes(bytes) {
-  let mb = bytes / 1024 / 1024;
+  const mb = bytes / 1024 / 1024;
   return `${Math.round(mb * 10) / 10} Mb`;
 }
 

lib/Browser.js

@@ -50,7 +50,7 @@ class Browser {
    * @return {!Promise<string>}
    */
   async version() {
-    let version = await this._connection.send('Browser.getVersion');
+    const version = await this._connection.send('Browser.getVersion');
     return version.product;
   }
 

lib/Connection.js

@@ -27,7 +27,7 @@ class Connection extends EventEmitter {
    */
   static async create(url, delay = 0) {
     return new Promise((resolve, reject) => {
-      let ws = new WebSocket(url, { perMessageDeflate: false });
+      const ws = new WebSocket(url, { perMessageDeflate: false });
       ws.on('open', () => resolve(new Connection(url, ws, delay)));
       ws.on('error', reject);
     });
@@ -66,8 +66,8 @@ class Connection extends EventEmitter {
    * @return {!Promise<?Object>}
    */
   send(method, params = {}) {
-    let id = ++this._lastId;
-    let message = JSON.stringify({id, method, params});
+    const id = ++this._lastId;
+    const message = JSON.stringify({id, method, params});
     debugProtocol('SEND ► ' + message);
     this._ws.send(message);
     return new Promise((resolve, reject) => {
@@ -82,9 +82,9 @@ class Connection extends EventEmitter {
     if (this._delay)
       await new Promise(f => setTimeout(f, this._delay));
     debugProtocol('◀ RECV ' + message);
-    let object = JSON.parse(message);
+    const object = JSON.parse(message);
     if (object.id && this._callbacks.has(object.id)) {
-      let callback = this._callbacks.get(object.id);
+      const callback = this._callbacks.get(object.id);
       this._callbacks.delete(object.id);
       if (object.error)
         callback.reject(new Error(`Protocol error (${callback.method}): ${object.error.message} ${object.error.data}`));
@@ -109,10 +109,10 @@ class Connection extends EventEmitter {
 
   _onClose() {
     this._ws.removeAllListeners();
-    for (let callback of this._callbacks.values())
+    for (const callback of this._callbacks.values())
       callback.reject(new Error(`Protocol error (${callback.method}): Target closed.`));
     this._callbacks.clear();
-    for (let session of this._sessions.values())
+    for (const session of this._sessions.values())
       session._onClosed();
     this._sessions.clear();
   }
@@ -168,14 +168,14 @@ class Session extends EventEmitter {
   send(method, params = {}) {
     if (!this._connection)
       return Promise.reject(new Error(`Protocol error (${method}): Session closed. Most likely the page has been closed.`));
-    let id = ++this._lastId;
-    let message = JSON.stringify({id, method, params});
+    const id = ++this._lastId;
+    const message = JSON.stringify({id, method, params});
     debugSession('SEND ► ' + message);
     this._connection.send('Target.sendMessageToTarget', {sessionId: this._sessionId, message}).catch(e => {
       // The response from target might have been already dispatched.
       if (!this._callbacks.has(id))
         return;
-      let callback = this._callbacks.get(id);
+      const callback = this._callbacks.get(id);
       this._callbacks.delete(object.id);
       callback.reject(e);
     });
@@ -189,9 +189,9 @@ class Session extends EventEmitter {
    */
   _onMessage(message) {
     debugSession('◀ RECV ' + message);
-    let object = JSON.parse(message);
+    const object = JSON.parse(message);
     if (object.id && this._callbacks.has(object.id)) {
-      let callback = this._callbacks.get(object.id);
+      const callback = this._callbacks.get(object.id);
       this._callbacks.delete(object.id);
       if (object.error)
         callback.reject(new Error(`Protocol error (${callback.method}): ${object.error.message} ${object.error.data}`));
@@ -211,7 +211,7 @@ class Session extends EventEmitter {
   }
 
   _onClosed() {
-    for (let callback of this._callbacks.values())
+    for (const callback of this._callbacks.values())
       callback.reject(new Error(`Protocol error (${callback.method}): Target closed.`));
     this._callbacks.clear();
     this._connection = null;

lib/ElementHandle.js

@@ -48,11 +48,11 @@ class ElementHandle {
     console.assert(!this._disposed, 'ElementHandle is disposed!');
     console.assert(typeof pageFunction === 'function', 'First argument to ElementHandle.evaluate must be a function!');
 
-    let stringifiedArgs = ['this'];
+    const stringifiedArgs = ['this'];
     stringifiedArgs.push(...args.map(x => JSON.stringify(x)));
-    let functionDeclaration = `function() { return (${pageFunction})(${stringifiedArgs.join(',')}) }`;
+    const functionDeclaration = `function() { return (${pageFunction})(${stringifiedArgs.join(',')}) }`;
     const objectId = this._remoteObject.objectId;
-    let { exceptionDetails, result: remoteObject } = await this._client.send('Runtime.callFunctionOn', { objectId, functionDeclaration, returnByValue: false, awaitPromise: true});
+    const { exceptionDetails, result: remoteObject } = await this._client.send('Runtime.callFunctionOn', { objectId, functionDeclaration, returnByValue: false, awaitPromise: true});
     if (exceptionDetails)
       throw new Error('Evaluation failed: ' + helper.getExceptionMessage(exceptionDetails));
     return await helper.serializeRemoteObject(this._client, remoteObject);
@@ -62,11 +62,11 @@ class ElementHandle {
    * @return {!Promise<{x: number, y: number}>}
    */
   async _visibleCenter() {
-    let center = await this.evaluate(element => {
+    const center = await this.evaluate(element => {
       if (!element.ownerDocument.contains(element))
         return null;
       element.scrollIntoViewIfNeeded();
-      let rect = element.getBoundingClientRect();
+      const rect = element.getBoundingClientRect();
       return {
         x: (Math.max(rect.left, 0) + Math.min(rect.right, window.innerWidth)) / 2,
         y: (Math.max(rect.top, 0) + Math.min(rect.bottom, window.innerHeight)) / 2
@@ -81,7 +81,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async hover() {
-    let {x, y} = await this._visibleCenter();
+    const {x, y} = await this._visibleCenter();
     await this._mouse.move(x, y);
   }
 
@@ -90,7 +90,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async click(options) {
-    let {x, y} = await this._visibleCenter();
+    const {x, y} = await this._visibleCenter();
     await this._mouse.click(x, y, options);
   }
 
@@ -99,7 +99,7 @@ class ElementHandle {
    * @return {!Promise}
    */
   async uploadFile(...filePaths) {
-    let files = filePaths.map(filePath => path.resolve(filePath));
+    const files = filePaths.map(filePath => path.resolve(filePath));
     const objectId = this._remoteObject.objectId;
     return this._client.send('DOM.setFileInputFiles', { objectId, files });
   }

lib/FrameManager.js

@@ -61,8 +61,8 @@ class FrameManager extends EventEmitter {
     if (this._frames.has(frameId))
       return;
     console.assert(parentFrameId);
-    let parentFrame = this._frames.get(parentFrameId);
-    let frame = new Frame(this._client, this._mouse, parentFrame, frameId);
+    const parentFrame = this._frames.get(parentFrameId);
+    const frame = new Frame(this._client, this._mouse, parentFrame, frameId);
     this._frames.set(frame._id, frame);
     this.emit(FrameManager.Events.FrameAttached, frame);
   }
@@ -77,7 +77,7 @@ class FrameManager extends EventEmitter {
 
     // Detach all child frames first.
     if (frame) {
-      for (let child of frame.childFrames())
+      for (const child of frame.childFrames())
         this._removeFramesRecursively(child);
     }
 
@@ -105,7 +105,7 @@ class FrameManager extends EventEmitter {
    * @param {string} frameId
    */
   _onFrameDetached(frameId) {
-    let frame = this._frames.get(frameId);
+    const frame = this._frames.get(frameId);
     if (frame)
       this._removeFramesRecursively(frame);
   }
@@ -116,15 +116,15 @@ class FrameManager extends EventEmitter {
     if (!frame)
       return;
     frame._defaultContextId = context.id;
-    for (let waitTask of frame._waitTasks)
+    for (const waitTask of frame._waitTasks)
       waitTask.rerun();
   }
 
   /**
    * @param {!Frame} frame
    */
   _removeFramesRecursively(frame) {
-    for (let child of frame.childFrames())
+    for (const child of frame.childFrames())
       this._removeFramesRecursively(child);
     frame._detach();
     this._frames.delete(frame._id);
@@ -179,7 +179,7 @@ class Frame {
    * @return {!Promise<(!Object|undefined)>}
    */
   async evaluate(pageFunction, ...args) {
-    let remoteObject = await this._rawEvaluate(pageFunction, ...args);
+    const remoteObject = await this._rawEvaluate(pageFunction, ...args);
     return await helper.serializeRemoteObject(this._client, remoteObject);
   }
 
@@ -188,7 +188,7 @@ class Frame {
    * @return {!Promise<?ElementHandle>}
    */
   async $(selector) {
-    let remoteObject = await this._rawEvaluate(selector => document.querySelector(selector), selector);
+    const remoteObject = await this._rawEvaluate(selector => document.querySelector(selector), selector);
     if (remoteObject.subtype === 'node')
       return new ElementHandle(this._client, remoteObject, this._mouse);
     helper.releaseObject(this._client, remoteObject);
@@ -201,9 +201,9 @@ class Frame {
    * @return {!Promise<(!Object|undefined)>}
    */
   async _rawEvaluate(pageFunction, ...args) {
-    let expression = helper.evaluationString(pageFunction, ...args);
+    const expression = helper.evaluationString(pageFunction, ...args);
     const contextId = this._defaultContextId;
-    let { exceptionDetails, result: remoteObject }  = await this._client.send('Runtime.evaluate', { expression, contextId, returnByValue: false, awaitPromise: true});
+    const { exceptionDetails, result: remoteObject }  = await this._client.send('Runtime.evaluate', { expression, contextId, returnByValue: false, awaitPromise: true});
     if (exceptionDetails)
       throw new Error('Evaluation failed: ' + helper.getExceptionMessage(exceptionDetails));
     return remoteObject;
@@ -270,9 +270,9 @@ class Frame {
      * @param {string} url
      */
     function addScriptTag(url) {
-      let script = document.createElement('script');
+      const script = document.createElement('script');
       script.src = url;
-      let promise = new Promise(x => script.onload = x);
+      const promise = new Promise(x => script.onload = x);
       document.head.appendChild(script);
       return promise;
     }
@@ -349,7 +349,7 @@ class Frame {
   }
 
   _detach() {
-    for (let waitTask of this._waitTasks)
+    for (const waitTask of this._waitTasks)
       waitTask.terminate(new Error('waitForSelector failed: frame got detached.'));
     this._detached = true;
     if (this._parentFrame)

lib/Input.js

@@ -166,7 +166,7 @@ class Mouse {
   }
 }
 
-let keys = {
+const keys = {
   'Cancel': 3,
   'Help': 6,
   'Backspace': 8,

lib/Launcher.js

@@ -113,7 +113,7 @@ class Launcher {
    * @return {!Promise<!Browser>}
    */
   static async connect({browserWSEndpoint, ignoreHTTPSErrors = false}) {
-    let connection = await Connection.create(browserWSEndpoint);
+    const connection = await Connection.create(browserWSEndpoint);
     return new Browser(connection, !!ignoreHTTPSErrors);
   }
 }
@@ -127,12 +127,12 @@ function waitForWSEndpoint(chromeProcess, timeout) {
   return new Promise((resolve, reject) => {
     const rl = readline.createInterface({ input: chromeProcess.stderr });
     let stderr = '';
-    let listeners = [
+    const listeners = [
       helper.addEventListener(rl, 'line', onLine),
       helper.addEventListener(rl, 'close', onClose),
       helper.addEventListener(chromeProcess, 'exit', onClose)
     ];
-    let timeoutId = timeout ? setTimeout(onTimeout, timeout) : 0;
+    const timeoutId = timeout ? setTimeout(onTimeout, timeout) : 0;
 
     function onClose() {
       cleanup();

lib/Multimap.js

@@ -61,7 +61,7 @@ class Multimap {
    * @return {boolean}
    */
   hasValue(key, value) {
-    let set = this._map.get(key);
+    const set = this._map.get(key);
     if (!set)
       return false;
     return set.has(value);
@@ -80,8 +80,8 @@ class Multimap {
    * @return {boolean}
    */
   delete(key, value) {
-    let values = this.get(key);
-    let result = values.delete(value);
+    const values = this.get(key);
+    const result = values.delete(value);
     if (!values.size)
       this._map.delete(key);
     return result;
@@ -99,7 +99,7 @@ class Multimap {
    * @return {?V} value
    */
   firstValue(key) {
-    let set = this._map.get(key);
+    const set = this._map.get(key);
     if (!set)
       return null;
     return set.values().next().value;
@@ -116,8 +116,8 @@ class Multimap {
    * @return {!Array<!V>}
    */
   valuesArray() {
-    let result = [];
-    for (let key of this._map.keys())
+    const result = [];
+    for (const key of this._map.keys())
       result.push(...Array.from(this._map.get(key).values()));
     return result;
   }

lib/NavigatorWatcher.js

@@ -40,19 +40,19 @@ class NavigatorWatcher {
 
     this._eventListeners = [];
 
-    let watchdog = new Promise(fulfill => this._maximumTimer = setTimeout(fulfill, this._timeout))
+    const watchdog = new Promise(fulfill => this._maximumTimer = setTimeout(fulfill, this._timeout))
         .then(() => 'Navigation Timeout Exceeded: ' + this._timeout + 'ms exceeded');
-    let navigationPromises = [watchdog];
+    const navigationPromises = [watchdog];
 
     if (!this._ignoreHTTPSErrors) {
-      let certificateError = new Promise(fulfill => {
+      const certificateError = new Promise(fulfill => {
         this._eventListeners.push(helper.addEventListener(this._client, 'Security.certificateError', fulfill));
       }).then(error => 'SSL Certificate error: ' + error.errorType);
       navigationPromises.push(certificateError);
     }
 
     if (this._waitUntil === 'load') {
-      let loadEventFired = new Promise(fulfill => {
+      const loadEventFired = new Promise(fulfill => {
         this._eventListeners.push(helper.addEventListener(this._client, 'Page.loadEventFired', fulfill));
       }).then(() => null);
       navigationPromises.push(loadEventFired);
@@ -64,7 +64,7 @@ class NavigatorWatcher {
         helper.addEventListener(this._client, 'Network.webSocketCreated', this._onLoadingStarted.bind(this)),
         helper.addEventListener(this._client, 'Network.webSocketClosed', this._onLoadingCompleted.bind(this)),
       ]);
-      let networkIdle = new Promise(fulfill => this._networkIdleCallback = fulfill).then(() => null);
+      const networkIdle = new Promise(fulfill => this._networkIdleCallback = fulfill).then(() => null);
       navigationPromises.push(networkIdle);
     }