eslint: Prefer const over let (#3650)

.eslintrc.js

@@ -47,6 +47,12 @@ module.exports = {
     // Allow debugger during development
     'no-debugger': process.env.NODE_ENV === 'production' ? 2 : 0,
 
+    // Prefer const over let
+    "prefer-const": ["error", {
+      "destructuring": "any",
+      "ignoreReadBeforeAssign": false
+    }],
+
     // Do not allow console.logs etc...
     'no-console': 2,
     'space-before-function-paren': [2, {

examples/async-data/pages/posts/_id.vue

@@ -13,7 +13,7 @@ import axios from 'axios'
 export default {
   async asyncData({ params }) {
     // We can use async/await ES6 feature
-    let { data } = await axios.get(`https://jsonplaceholder.typicode.com/posts/${params.id}`)
+    const { data } = await axios.get(`https://jsonplaceholder.typicode.com/posts/${params.id}`)
     return { post: data }
   },
   head() {

examples/custom-server/server.js

@@ -7,7 +7,7 @@ const host = process.env.HOST || '127.0.0.1'
 const port = process.env.PORT || 3000
 
 // Import and set Nuxt.js options
-let config = require('./nuxt.config.js')
+const config = require('./nuxt.config.js')
 config.dev = !(process.env.NODE_ENV === 'production')
 
 const nuxt = new Nuxt(config)

examples/dynamic-layouts/middleware/mobile.js

@@ -1,4 +1,4 @@
 export default function (ctx) {
-  let userAgent = ctx.req ? ctx.req.headers['user-agent'] : navigator.userAgent
+  const userAgent = ctx.req ? ctx.req.headers['user-agent'] : navigator.userAgent
   ctx.isMobile = /mobile/i.test(userAgent)
 }

examples/storybook/stories/Logo.story.js

@@ -35,7 +35,7 @@ nStoriesOf({ Logo }, 'Logo ')
   }))
   .addVT('with App layout', '<logo :data="{  }  "/>')
   .addVT('with a knob', () => {
-    let data = JSON.stringify(
+    const data = JSON.stringify(
       object('Data', {
         name: 'Apple',
         count: 132

examples/storybook/stories/storybase.js

@@ -37,7 +37,7 @@ const vtmp = (cmp, cmpStr) => ({
  * @param {*} params
  */
 const nStoriesOf = (cmp, name = Object.keys(cmp)[0], params = {}) => {
-  let x = storiesOf(name, module)
+  const x = storiesOf(name, module)
     .addDecorator(centered)
     .addDecorator(withKnobs)
 

examples/with-sockets/io/index.js

@@ -11,7 +11,7 @@ export default function () {
   this.nuxt.hook('close', () => new Promise(server.close))
 
   // Add socket.io events
-  let messages = []
+  const messages = []
   io.on('connection', (socket) => {
     socket.on('last-messages', function (fn) {
       fn(messages.slice(-50))

examples/with-sockets/pages/index.vue

@@ -41,7 +41,7 @@ export default {
   methods: {
     sendMessage() {
       if (!this.message.trim()) return
-      let message = {
+      const message = {
         date: new Date().toJSON(),
         text: this.message.trim()
       }

examples/with-sockets/server.js

@@ -12,7 +12,7 @@ const server = http.createServer(app)
 const io = SocketIO(server)
 
 // We instantiate Nuxt.js with the options
-let config = require('./nuxt.config.js')
+const config = require('./nuxt.config.js')
 config.dev = !isProd
 
 const nuxt = new Nuxt(config)
@@ -28,7 +28,7 @@ server.listen(port, '0.0.0.0')
 console.log('Server listening on localhost:' + port) // eslint-disable-line no-console
 
 // Socket.io
-let messages = []
+const messages = []
 io.on('connection', (socket) => {
   socket.on('last-messages', function (fn) {
     fn(messages.slice(-50))

lib/builder/builder.js

@@ -113,7 +113,7 @@ export default class Builder {
     this._nuxtPages = typeof this.options.build.createRoutes !== 'function'
     if (this._nuxtPages) {
       if (!fsExtra.existsSync(path.join(this.options.srcDir, this.options.dir.pages))) {
-        let dir = this.options.srcDir
+        const dir = this.options.srcDir
         if (fsExtra.existsSync(path.join(this.options.srcDir, '..', this.options.dir.pages))) {
           throw new Error(
             `No \`${this.options.dir.pages}\` directory found in ${dir}. Did you mean to run \`nuxt\` in the parent (\`../\`) directory?`
@@ -215,7 +215,7 @@ export default class Builder {
       })
       let hasErrorLayout = false
       layoutsFiles.forEach((file) => {
-        let name = file
+        const name = file
           .split('/')
           .slice(1)
           .join('/')

lib/builder/generator.js

@@ -96,7 +96,7 @@ export default class Generator {
   }
 
   async generateRoutes(routes) {
-    let errors = []
+    const errors = []
 
     // Start generate process
     while (routes.length) {
@@ -139,7 +139,7 @@ export default class Generator {
   }
 
   async afterGenerate() {
-    let { fallback } = this.options.generate
+    const { fallback } = this.options.generate
 
     // Disable SPA fallback if value isn't true or a string
     if (fallback !== true && typeof fallback !== 'string') return
@@ -193,7 +193,7 @@ export default class Generator {
   }
 
   decorateWithPayloads(routes, generateRoutes) {
-    let routeMap = {}
+    const routeMap = {}
     // Fill routeMap for known routes
     routes.forEach((route) => {
       routeMap[route] = { route, payload: null }

lib/builder/webpack/base.js

@@ -142,7 +142,7 @@ export default class WebpackBaseConfig {
         exclude: (file) => {
           // not exclude files outside node_modules
           if (/node_modules/.test(file)) {
-            for (let module of [/\.vue\.js/].concat(this.options.build.transpile)) {
+            for (const module of [/\.vue\.js/].concat(this.options.build.transpile)) {
               // item in transpile can be string or regex object
               if (module.test(file)) {
                 return false

lib/builder/webpack/utils/postcss.js

@@ -55,8 +55,8 @@ export default class PostcssConfig {
   configFromFile() {
     // Search for postCSS config file and use it if exists
     // https://github.com/michael-ciniawsky/postcss-load-config
-    for (let dir of [this.srcDir, this.rootDir]) {
-      for (let file of [
+    for (const dir of [this.srcDir, this.rootDir]) {
+      for (const file of [
         'postcss.config.js',
         '.postcssrc.js',
         '.postcssrc',

lib/common/utils.js

@@ -99,7 +99,7 @@ export const chainFn = function chainFn(base, fn) {
     if (baseResult === undefined) {
       baseResult = arguments[0]
     }
-    let fnResult = fn.call(
+    const fnResult = fn.call(
       this,
       baseResult,
       ...Array.prototype.slice.call(arguments, 1)
@@ -139,8 +139,8 @@ const sysSep = _.escapeRegExp(path.sep)
 const normalize = string => string.replace(reqSep, sysSep)
 
 export const r = function r() {
-  let args = Array.prototype.slice.apply(arguments)
-  let lastArg = _.last(args)
+  const args = Array.prototype.slice.apply(arguments)
+  const lastArg = _.last(args)
 
   if (lastArg.indexOf('@') === 0 || lastArg.indexOf('~') === 0) {
     return wp(lastArg)
@@ -150,8 +150,8 @@ export const r = function r() {
 }
 
 export const relativeTo = function relativeTo() {
-  let args = Array.prototype.slice.apply(arguments)
-  let dir = args.shift()
+  const args = Array.prototype.slice.apply(arguments)
+  const dir = args.shift()
 
   // Keep webpack inline loader intact
   if (args[0].indexOf('!') !== -1) {
@@ -161,7 +161,7 @@ export const relativeTo = function relativeTo() {
   }
 
   // Resolve path
-  let _path = r(...args)
+  const _path = r(...args)
 
   // Check if path is an alias
   if (_path.indexOf('@') === 0 || _path.indexOf('~') === 0) {
@@ -201,12 +201,12 @@ export const flatRoutes = function flatRoutes(router, _path = '', routes = []) {
 
 function cleanChildrenRoutes(routes, isChild = false) {
   let start = -1
-  let routesIndex = []
+  const routesIndex = []
   routes.forEach((route) => {
     if (/-index$/.test(route.name) || route.name === 'index') {
       // Save indexOf 'index' key in name
-      let res = route.name.split('-')
-      let s = res.indexOf('index')
+      const res = route.name.split('-')
+      const s = res.indexOf('index')
       start = start === -1 || s < start ? s : start
       routesIndex.push(res)
     }
@@ -214,13 +214,13 @@ function cleanChildrenRoutes(routes, isChild = false) {
   routes.forEach((route) => {
     route.path = isChild ? route.path.replace('/', '') : route.path
     if (route.path.indexOf('?') > -1) {
-      let names = route.name.split('-')
-      let paths = route.path.split('/')
+      const names = route.name.split('-')
+      const paths = route.path.split('/')
       if (!isChild) {
         paths.shift()
       } // clean first / for parents
       routesIndex.forEach((r) => {
-        let i = r.indexOf('index') - start //  children names
+        const i = r.indexOf('index') - start //  children names
         if (i < paths.length) {
           for (let a = 0; a <= i; a++) {
             if (a === i) {
@@ -246,15 +246,15 @@ function cleanChildrenRoutes(routes, isChild = false) {
 }
 
 export const createRoutes = function createRoutes(files, srcDir, pagesDir) {
-  let routes = []
+  const routes = []
   files.forEach((file) => {
-    let keys = file
+    const keys = file
       .replace(RegExp(`^${pagesDir}`), '')
       .replace(/\.(vue|js)$/, '')
       .replace(/\/{2,}/g, '/')
       .split('/')
       .slice(1)
-    let route = { name: '', path: '', component: r(srcDir, file) }
+    const route = { name: '', path: '', component: r(srcDir, file) }
     let parent = routes
     keys.forEach((key, i) => {
       // remove underscore only, if its the prefix
@@ -266,7 +266,7 @@ export const createRoutes = function createRoutes(files, srcDir, pagesDir) {
         : sanitizedKey
       route.name += key === '_' ? 'all' : ''
       route.chunkName = file.replace(/\.(vue|js)$/, '')
-      let child = _.find(parent, { name: route.name })
+      const child = _.find(parent, { name: route.name })
       if (child) {
         child.children = child.children || []
         parent = child.children

lib/core/middleware/error.js

@@ -89,9 +89,9 @@ async function readSource(frame) {
   ]
 
   // Scan filesystem for real source
-  for (let pathDir of searchPath) {
-    let fullPath = path.resolve(pathDir, frame.fileName)
-    let source = await fs.readFile(fullPath, 'utf-8').catch(() => null)
+  for (const pathDir of searchPath) {
+    const fullPath = path.resolve(pathDir, frame.fileName)
+    const source = await fs.readFile(fullPath, 'utf-8').catch(() => null)
     if (source) {
       frame.contents = source
       frame.fullPath = fullPath

lib/core/nuxt.js

@@ -205,7 +205,7 @@ export default class Nuxt {
       return _path
     }
 
-    for (let ext of this.options.extensions) {
+    for (const ext of this.options.extensions) {
       if (fs.existsSync(_path + '.' + ext)) {
         return _path + '.' + ext
       }

lib/core/renderer.js

@@ -61,23 +61,22 @@ export default class Renderer {
   }
 
   async loadResources(_fs = fs) {
-    let distPath = path.resolve(this.options.buildDir, 'dist')
-    let updated = []
+    const distPath = path.resolve(this.options.buildDir, 'dist')
+    const updated = []
 
     resourceMap.forEach(({ key, fileName, transform }) => {
-      let rawKey = '$$' + key
+      const rawKey = '$$' + key
       const _path = path.join(distPath, fileName)
 
-      let rawData, data
       if (!_fs.existsSync(_path)) {
         return // Resource not exists
       }
-      rawData = _fs.readFileSync(_path, 'utf8')
+      const rawData = _fs.readFileSync(_path, 'utf8')
       if (!rawData || rawData === this.resources[rawKey]) {
         return // No changes
       }
       this.resources[rawKey] = rawData
-      data = transform(rawData)
+      const data = transform(rawData)
       /* istanbul ignore if */
       if (!data) {
         return // Invalid data ?
@@ -371,7 +370,7 @@ export default class Renderer {
     const cspScriptSrcHashSet = new Set()
     if (this.options.render.csp) {
       const { hashAlgorithm } = this.options.render.csp
-      let hash = crypto.createHash(hashAlgorithm)
+      const hash = crypto.createHash(hashAlgorithm)
       hash.update(serializedSession)
       cspScriptSrcHashSet.add(`'${hashAlgorithm}-${hash.digest('base64')}'`)
     }
@@ -414,7 +413,7 @@ export default class Renderer {
         throw e
       }
     }
-    let options = {
+    const options = {
       resources: 'usable', // load subresources (https://github.com/tmpvar/jsdom#loading-subresources)
       runScripts: 'dangerously',
       beforeParse(window) {
@@ -436,7 +435,7 @@ export default class Renderer {
     )
     /* istanbul ignore if */
     if (!nuxtExists) {
-      let error = new Error('Could not load the nuxt app')
+      const error = new Error('Could not load the nuxt app')
       error.body = window.document.body.innerHTML
       throw error
     }

test/e2e/basic.browser.test.js

@@ -29,7 +29,7 @@ describe('basic browser', () => {
 
   test('/noloading', async () => {
     const { hook } = await page.nuxt.navigate('/noloading')
-    let loading = await page.nuxt.loadingData()
+    const loading = await page.nuxt.loadingData()
     expect(loading.show).toBe(true)
     await hook
     expect(loading.show).toBe(true)

test/unit/dynamic-routes.test.js

@@ -18,7 +18,7 @@ describe('dynamic routes', () => {
         routerFile.indexOf('['),
         routerFile.lastIndexOf(']') + 1
       )
-      let routes = eval('( ' + routerFile + ')') // eslint-disable-line no-eval
+      const routes = eval('( ' + routerFile + ')') // eslint-disable-line no-eval
       // pages/test/index.vue
       expect(routes[0].path).toBe('/test')
       expect(routes[0].name).toBe('test')

test/unit/error.test.js

@@ -23,7 +23,7 @@ describe('error', () => {
   })
 
   test('/404 should display an error too', async () => {
-    let { error } = await nuxt.renderRoute('/404')
+    const { error } = await nuxt.renderRoute('/404')
     expect(error.message.includes('This page could not be found')).toBe(true)
   })
 

test/unit/module.test.js

@@ -45,12 +45,12 @@ describe('module', () => {
   // })
 
   test('Middleware', async () => {
-    let response = await rp(url('/api'))
+    const response = await rp(url('/api'))
     expect(response).toBe('It works!')
   })
 
   test('Hooks - Use external middleware before render', async () => {
-    let response = await rp(url('/use-middleware'))
+    const response = await rp(url('/use-middleware'))
     expect(response).toBe('Use external middleware')
   })
 

test/unit/nuxt.test.js

@@ -26,7 +26,7 @@ describe('nuxt', () => {
     })
 
     return new Builder(nuxt).build().catch((err) => {
-      let s = String(err)
+      const s = String(err)
       expect(s.includes('No `pages` directory found')).toBe(true)
       expect(s.includes('Did you mean to run `nuxt` in the parent (`../`) directory?')).toBe(true)
     })

test/unit/ssr.test.js

@@ -19,15 +19,15 @@ const url = route => 'http://localhost:' + port + route
 // We strictly compare <foorbar>{id}</foorbar> section
 // Because other response parts such as window.__NUXT may be different resulting false positive passes.
 const uniqueTest = async (url) => {
-  let results = []
+  const results = []
 
   await Utils.parallel(range(5), async () => {
-    let { html } = await nuxt.renderRoute(url)
-    let foobar = match(FOOBAR_REGEX, html)
+    const { html } = await nuxt.renderRoute(url)
+    const foobar = match(FOOBAR_REGEX, html)
     results.push(parseInt(foobar))
   })
 
-  let isUnique = uniq(results).length === results.length
+  const isUnique = uniq(results).length === results.length
 
   if (!isUnique) {
     /* eslint-disable no-console */
@@ -44,13 +44,13 @@ const uniqueTest = async (url) => {
 // Or pending promises/sockets and function calls.
 // Related issue: https://github.com/nuxt/nuxt.js/issues/1354
 const stressTest = async (_url, concurrency = 2, steps = 4) => {
-  let statusCodes = {}
+  const statusCodes = {}
 
   await Utils.sequence(range(steps), async () => {
     await Utils.parallel(range(concurrency), async () => {
-      let response = await rp(url(_url), { resolveWithFullResponse: true })
+      const response = await rp(url(_url), { resolveWithFullResponse: true })
       // Status Code
-      let code = response.statusCode
+      const code = response.statusCode
       if (!statusCodes[code]) {
         statusCodes[code] = 0
       }

test/unit/utils.test.js

@@ -8,7 +8,7 @@ describe('utils', () => {
   })
 
   test('getContext', () => {
-    let ctx = Utils.getContext({ a: 1 }, { b: 2 })
+    const ctx = Utils.getContext({ a: 1 }, { b: 2 })
     expect(Utils.getContext.length).toBe(2)
     expect(typeof ctx.req).toBe('object')
     expect(typeof ctx.res).toBe('object')
@@ -17,7 +17,7 @@ describe('utils', () => {
   })
 
   test.skip.appveyor('waitFor', async () => {
-    let s = Date.now()
+    const s = Date.now()
     await Utils.waitFor(100)
     expect(Date.now() - s >= 100).toBe(true)
     await Utils.waitFor()

test/utils/mock-log.js

@@ -6,17 +6,17 @@ export default function mockLog(levels = 'all', logger = console) {
     levels = [levels]
   }
   beforeAll(() => {
-    for (let level of levels) {
+    for (const level of levels) {
       jest.spyOn(logger, level).mockImplementation(() => {})
     }
   })
   beforeEach(() => {
-    for (let level of levels) {
+    for (const level of levels) {
       logger[level].mockClear()
     }
   })
   afterAll(() => {
-    for (let level of levels) {
+    for (const level of levels) {
       logger[level].mockRestore()
     }
   })