refactor: add prefer-const to .eslintrc + fix errors (#14880)

lib/browser/api/app.js

@@ -42,7 +42,7 @@ Object.assign(app, {
 
 const nativeFn = app.getAppMetrics
 app.getAppMetrics = () => {
-  let metrics = nativeFn.call(app)
+  const metrics = nativeFn.call(app)
   for (const metric of metrics) {
     if ('memory' in metric) {
       deprecate.removeProperty(metric, 'memory')
@@ -96,7 +96,7 @@ app.allowNTLMCredentialsForAllDomains = function (allow) {
   if (!process.noDeprecations) {
     deprecate.warn('app.allowNTLMCredentialsForAllDomains', 'session.allowNTLMCredentialsForDomains')
   }
-  let domains = allow ? '*' : ''
+  const domains = allow ? '*' : ''
   if (!this.isReady()) {
     this.commandLine.appendSwitch('auth-server-whitelist', domains)
   } else {
@@ -106,7 +106,7 @@ app.allowNTLMCredentialsForAllDomains = function (allow) {
 
 // Routes the events to webContents.
 const events = ['login', 'certificate-error', 'select-client-certificate']
-for (let name of events) {
+for (const name of events) {
   app.on(name, (event, webContents, ...args) => {
     webContents.emit(name, event, ...args)
   })

lib/browser/api/auto-updater/squirrel-update-win.js

@@ -17,7 +17,7 @@ const isSameArgs = (args) => args.length === spawnedArgs.length && args.every((e
 
 // Spawn a command and invoke the callback when it completes with an error
 // and the output from standard out.
-let spawnUpdate = function (args, detached, callback) {
+const spawnUpdate = function (args, detached, callback) {
   let error, errorEmitted, stderr, stdout
 
   try {

lib/browser/api/browser-window.js

@@ -41,14 +41,14 @@ BrowserWindow.prototype._init = function () {
   this.webContents.on('-add-new-contents', (event, webContents, disposition,
     userGesture, left, top, width,
     height) => {
-    let urlFrameName = v8Util.getHiddenValue(webContents, 'url-framename')
+    const urlFrameName = v8Util.getHiddenValue(webContents, 'url-framename')
     if ((disposition !== 'foreground-tab' && disposition !== 'new-window' &&
          disposition !== 'background-tab') || !urlFrameName) {
       event.preventDefault()
       return
     }
 
-    let { url, frameName } = urlFrameName
+    const { url, frameName } = urlFrameName
     v8Util.deleteHiddenValue(webContents, 'url-framename')
     const options = {
       show: true,
@@ -115,7 +115,7 @@ BrowserWindow.prototype._init = function () {
   }
 
   const visibilityEvents = ['show', 'hide', 'minimize', 'maximize', 'restore']
-  for (let event of visibilityEvents) {
+  for (const event of visibilityEvents) {
     this.on(event, visibilityChanged)
   }
 
@@ -145,7 +145,7 @@ BrowserWindow.getAllWindows = () => {
 }
 
 BrowserWindow.getFocusedWindow = () => {
-  for (let window of BrowserWindow.getAllWindows()) {
+  for (const window of BrowserWindow.getAllWindows()) {
     if (window.isFocused() || window.isDevToolsFocused()) return window
   }
   return null

lib/browser/api/dialog.js

@@ -284,7 +284,7 @@ module.exports = {
   },
 
   showCertificateTrustDialog: function (...args) {
-    let [window, options, callback] = parseArgs(...args)
+    const [window, options, callback] = parseArgs(...args)
 
     if (options == null || typeof options !== 'object') {
       throw new TypeError('options must be an object')

lib/browser/api/menu-item.js

@@ -8,7 +8,7 @@ const MenuItem = function (options) {
   const { Menu } = require('electron')
 
   // Preserve extra fields specified by user
-  for (let key in options) {
+  for (const key in options) {
     if (!(key in this)) this[key] = options[key]
   }
   if (typeof this.role === 'string' || this.role instanceof String) {

lib/browser/api/menu.js

@@ -180,7 +180,7 @@ function areValidTemplateItems (template) {
 
 function sortTemplate (template) {
   const sorted = sortMenuItems(template)
-  for (let id in sorted) {
+  for (const id in sorted) {
     const item = sorted[id]
     if (Array.isArray(item.submenu)) {
       item.submenu = sortTemplate(item.submenu)

lib/browser/api/navigation-controller.js

@@ -141,11 +141,10 @@ const NavigationController = (function () {
   }
 
   NavigationController.prototype.goToOffset = function (offset) {
-    let pendingIndex
     if (!this.canGoToOffset(offset)) {
       return
     }
-    pendingIndex = this.currentIndex + offset
+    const pendingIndex = this.currentIndex + offset
     if (this.inPageIndex > -1 && pendingIndex >= this.inPageIndex) {
       this.pendingIndex = pendingIndex
       return this.webContents._goToOffset(offset)

lib/browser/api/net.js

@@ -119,7 +119,7 @@ class ClientRequest extends EventEmitter {
     let urlStr = options.url
 
     if (!urlStr) {
-      let urlObj = {}
+      const urlObj = {}
       const protocol = options.protocol || 'http:'
       if (!kSupportedProtocols.has(protocol)) {
         throw new Error('Protocol "' + protocol + '" not supported. ')
@@ -149,7 +149,7 @@ class ClientRequest extends EventEmitter {
         // an invalid request.
         throw new TypeError('Request path contains unescaped characters.')
       }
-      let pathObj = url.parse(options.path || '/')
+      const pathObj = url.parse(options.path || '/')
       urlObj.pathname = pathObj.pathname
       urlObj.search = pathObj.search
       urlObj.hash = pathObj.hash
@@ -161,7 +161,7 @@ class ClientRequest extends EventEmitter {
       throw new Error('redirect mode should be one of follow, error or manual')
     }
 
-    let urlRequestOptions = {
+    const urlRequestOptions = {
       method: method,
       url: urlStr,
       redirect: redirectPolicy
@@ -180,7 +180,7 @@ class ClientRequest extends EventEmitter {
       }
     }
 
-    let urlRequest = new URLRequest(urlRequestOptions)
+    const urlRequest = new URLRequest(urlRequestOptions)
 
     // Set back and forward links.
     this.urlRequest = urlRequest
@@ -192,7 +192,7 @@ class ClientRequest extends EventEmitter {
     this.extraHeaders = {}
 
     if (options.headers) {
-      for (let key in options.headers) {
+      for (const key in options.headers) {
         this.setHeader(key, options.headers[key])
       }
     }
@@ -286,8 +286,8 @@ class ClientRequest extends EventEmitter {
   }
 
   _write (chunk, encoding, callback, isLast) {
-    let chunkIsString = typeof chunk === 'string'
-    let chunkIsBuffer = chunk instanceof Buffer
+    const chunkIsString = typeof chunk === 'string'
+    const chunkIsBuffer = chunk instanceof Buffer
     if (!chunkIsString && !chunkIsBuffer) {
       throw new TypeError('First argument must be a string or Buffer.')
     }
@@ -306,7 +306,7 @@ class ClientRequest extends EventEmitter {
 
     // Headers are assumed to be sent on first call to _writeBuffer,
     // i.e. after the first call to write or end.
-    let result = this.urlRequest.write(chunk, isLast)
+    const result = this.urlRequest.write(chunk, isLast)
 
     // The write callback is fired asynchronously to mimic Node.js.
     if (callback) {
@@ -318,7 +318,7 @@ class ClientRequest extends EventEmitter {
 
   write (data, encoding, callback) {
     if (this.urlRequest.finished) {
-      let error = new Error('Write after end.')
+      const error = new Error('Write after end.')
       process.nextTick(writeAfterEndNT, this, error, callback)
       return true
     }

lib/browser/api/web-contents.js

@@ -317,7 +317,7 @@ module.exports = {
 
   getFocusedWebContents () {
     let focused = null
-    for (let contents of binding.getAllWebContents()) {
+    for (const contents of binding.getAllWebContents()) {
       if (!contents.isFocused()) continue
       if (focused == null) focused = contents
       // Return webview web contents which may be embedded inside another