diff --git a/lib/browser/chrome-extension.js b/lib/browser/chrome-extension.js
index 4626270a8740..aa72552d0f63 100644
--- a/lib/browser/chrome-extension.js
+++ b/lib/browser/chrome-extension.js
@@ -9,11 +9,11 @@ const objectValues = function (object) {
 }
 
 // Mapping between hostname and file path.
-let hostPathMap = {}
+const hostPathMap = {}
 let hostPathMapNextKey = 0
 
 const generateHostForPath = function (path) {
-  let key = `extension-${++hostPathMapNextKey}`
+  const key = `extension-${++hostPathMapNextKey}`
   hostPathMap[key] = path
   return key
 }
@@ -23,10 +23,10 @@ const getPathForHost = function (host) {
 }
 
 // Cache manifests.
-let manifestMap = {}
+const manifestMap = {}
 
 const getManifestFromPath = function (srcDirectory) {
-  let manifest = JSON.parse(fs.readFileSync(path.join(srcDirectory, 'manifest.json')))
+  const manifest = JSON.parse(fs.readFileSync(path.join(srcDirectory, 'manifest.json')))
   if (!manifestMap[manifest.name]) {
     const hostname = generateHostForPath(srcDirectory)
     manifestMap[manifest.name] = manifest
@@ -47,7 +47,7 @@ const getManifestFromPath = function (srcDirectory) {
 }
 
 // Manage the background pages.
-let backgroundPages = {}
+const backgroundPages = {}
 
 const startBackgroundPages = function (manifest) {
   if (backgroundPages[manifest.hostname] || !manifest.background) return
@@ -82,7 +82,7 @@ const manifestToExtensionInfo = function (manifest) {
 const loadDevToolsExtensions = function (win, manifests) {
   if (!win.devToolsWebContents) return
 
-  for (let manifest of manifests) {
+  for (const manifest of manifests) {
     startBackgroundPages(manifest)
   }
   const extensionInfoArray = manifests.map(manifestToExtensionInfo)
@@ -94,7 +94,7 @@ let loadedExtensionsPath = null
 
 app.on('will-quit', function () {
   try {
-    let loadedExtensions = objectValues(manifestMap).map(function (manifest) {
+    const loadedExtensions = objectValues(manifestMap).map(function (manifest) {
       return manifest.srcDirectory
     })
     if (loadedExtensions.length > 0) {
@@ -117,10 +117,10 @@ app.once('ready', function () {
   // Load persisted extensions.
   loadedExtensionsPath = path.join(app.getPath('userData'), 'DevTools Extensions')
   try {
-    let loadedExtensions = JSON.parse(fs.readFileSync(loadedExtensionsPath))
+    const loadedExtensions = JSON.parse(fs.readFileSync(loadedExtensionsPath))
     if (Array.isArray(loadedExtensions)) {
       // Preheat the manifest cache.
-      for (let srcDirectory of loadedExtensions) {
+      for (const srcDirectory of loadedExtensions) {
         getManifestFromPath(srcDirectory)
       }
     }
@@ -130,11 +130,11 @@ app.once('ready', function () {
 
   // The chrome-extension: can map a extension URL request to real file path.
   const chromeExtensionHandler = function (request, callback) {
-    let parsed = url.parse(request.url)
+    const parsed = url.parse(request.url)
     if (!parsed.hostname || !parsed.path) return callback()
     if (!/extension-\d+/.test(parsed.hostname)) return callback()
 
-    let directory = getPathForHost(parsed.hostname)
+    const directory = getPathForHost(parsed.hostname)
     if (!directory) return callback()
 
     if (parsed.path === '/_generated_background_page.html' &&
@@ -146,10 +146,11 @@ app.once('ready', function () {
     }
 
     fs.readFile(path.join(directory, parsed.path), function (err, content) {
-      if (err)
-        callback(-6)  // FILE_NOT_FOUND
-      else
+      if (err) {
+        return callback(-6)  // FILE_NOT_FOUND
+      } else {
         return callback({mimeType: 'text/html', data: content})
+      }
     })
   }
   protocol.registerBufferProtocol('chrome-extension', chromeExtensionHandler, function (error) {
@@ -161,7 +162,7 @@ app.once('ready', function () {
   BrowserWindow.addDevToolsExtension = function (srcDirectory) {
     const manifest = getManifestFromPath(srcDirectory)
     if (manifest) {
-      for (let win of BrowserWindow.getAllWindows()) {
+      for (const win of BrowserWindow.getAllWindows()) {
         loadDevToolsExtensions(win, [manifest])
       }
       return manifest.name
@@ -172,7 +173,7 @@ app.once('ready', function () {
   }
 
   // Load persisted extensions when devtools is opened.
-  let init = BrowserWindow.prototype._init
+  const init = BrowserWindow.prototype._init
   BrowserWindow.prototype._init = function () {
     init.call(this)
     this.webContents.on('devtools-opened', () => {