Update variables to ES6 (#2169)

* Update variables to ES6

* Fix var for sanityError

* Fix var unexpectedKeyCache

* Add eslint rules

Author: davidrbright

.eslintrc

@@ -2,8 +2,8 @@
   "extends": "rackt",
   "rules": {
     "valid-jsdoc": 2,
-    // Disable until Flow supports let and const
-    "no-var": 0,
+    "no-var": 2,
+    "prefer-const": 2,
     "react/jsx-uses-react": 1,
     "react/jsx-no-undef": 2,
     "react/wrap-multilines": 2

build/use-lodash-es.js

@@ -2,7 +2,7 @@ module.exports = function () {
   return {
     visitor: {
       ImportDeclaration(path) {
-        var source = path.node.source
+        const source = path.node.source
         source.value = source.value.replace(/^lodash($|\/)/, 'lodash-es$1')
       }
     }

src/applyMiddleware.js

@@ -18,11 +18,11 @@ import compose from './compose'
  */
 export default function applyMiddleware(...middlewares) {
   return (createStore) => (reducer, preloadedState, enhancer) => {
-    var store = createStore(reducer, preloadedState, enhancer)
-    var dispatch = store.dispatch
-    var chain = []
+    const store = createStore(reducer, preloadedState, enhancer)
+    let dispatch = store.dispatch
+    let chain = []
 
-    var middlewareAPI = {
+    const middlewareAPI = {
       getState: store.getState,
       dispatch: (action) => dispatch(action)
     }

src/bindActionCreators.js

@@ -35,11 +35,11 @@ export default function bindActionCreators(actionCreators, dispatch) {
     )
   }
 
-  var keys = Object.keys(actionCreators)
-  var boundActionCreators = {}
-  for (var i = 0; i < keys.length; i++) {
-    var key = keys[i]
-    var actionCreator = actionCreators[key]
+  const keys = Object.keys(actionCreators)
+  const boundActionCreators = {}
+  for (let i = 0; i < keys.length; i++) {
+    const key = keys[i]
+    const actionCreator = actionCreators[key]
     if (typeof actionCreator === 'function') {
       boundActionCreators[key] = bindActionCreator(actionCreator, dispatch)
     }

src/combineReducers.js

@@ -2,11 +2,11 @@ import { ActionTypes } from './createStore'
 import isPlainObject from 'lodash/isPlainObject'
 import warning from './utils/warning'
 
-var NODE_ENV = typeof process !== 'undefined' ? process.env.NODE_ENV : 'development'
+const NODE_ENV = typeof process !== 'undefined' ? process.env.NODE_ENV : 'development'
 
 function getUndefinedStateErrorMessage(key, action) {
-  var actionType = action && action.type
-  var actionName = actionType && `"${actionType.toString()}"` || 'an action'
+  const actionType = action && action.type
+  const actionName = actionType && `"${actionType.toString()}"` || 'an action'
 
   return (
     `Given action ${actionName}, reducer "${key}" returned undefined. ` +
@@ -15,8 +15,8 @@ function getUndefinedStateErrorMessage(key, action) {
 }
 
 function getUnexpectedStateShapeWarningMessage(inputState, reducers, action, unexpectedKeyCache) {
-  var reducerKeys = Object.keys(reducers)
-  var argumentName = action && action.type === ActionTypes.INIT ?
+  const reducerKeys = Object.keys(reducers)
+  const argumentName = action && action.type === ActionTypes.INIT ?
     'preloadedState argument passed to createStore' :
     'previous state received by the reducer'
 
@@ -36,7 +36,7 @@ function getUnexpectedStateShapeWarningMessage(inputState, reducers, action, une
     )
   }
 
-  var unexpectedKeys = Object.keys(inputState).filter(key =>
+  const unexpectedKeys = Object.keys(inputState).filter(key =>
     !reducers.hasOwnProperty(key) &&
     !unexpectedKeyCache[key]
   )
@@ -57,8 +57,8 @@ function getUnexpectedStateShapeWarningMessage(inputState, reducers, action, une
 
 function assertReducerSanity(reducers) {
   Object.keys(reducers).forEach(key => {
-    var reducer = reducers[key]
-    var initialState = reducer(undefined, { type: ActionTypes.INIT })
+    const reducer = reducers[key]
+    const initialState = reducer(undefined, { type: ActionTypes.INIT })
 
     if (typeof initialState === 'undefined') {
       throw new Error(
@@ -69,7 +69,7 @@ function assertReducerSanity(reducers) {
       )
     }
 
-    var type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.')
+    const type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.')
     if (typeof reducer(undefined, { type }) === 'undefined') {
       throw new Error(
         `Reducer "${key}" returned undefined when probed with a random type. ` +
@@ -100,10 +100,10 @@ function assertReducerSanity(reducers) {
  * passed object, and builds a state object with the same shape.
  */
 export default function combineReducers(reducers) {
-  var reducerKeys = Object.keys(reducers)
-  var finalReducers = {}
-  for (var i = 0; i < reducerKeys.length; i++) {
-    var key = reducerKeys[i]
+  const reducerKeys = Object.keys(reducers)
+  const finalReducers = {}
+  for (let i = 0; i < reducerKeys.length; i++) {
+    const key = reducerKeys[i]
 
     if (NODE_ENV !== 'production') {
       if (typeof reducers[key] === 'undefined') {
@@ -115,13 +115,14 @@ export default function combineReducers(reducers) {
       finalReducers[key] = reducers[key]
     }
   }
-  var finalReducerKeys = Object.keys(finalReducers)
+  const finalReducerKeys = Object.keys(finalReducers)
 
+  let unexpectedKeyCache
   if (NODE_ENV !== 'production') {
-    var unexpectedKeyCache = {}
+    unexpectedKeyCache = {}
   }
 
-  var sanityError
+  let sanityError
   try {
     assertReducerSanity(finalReducers)
   } catch (e) {
@@ -134,21 +135,21 @@ export default function combineReducers(reducers) {
     }
 
     if (NODE_ENV !== 'production') {
-      var warningMessage = getUnexpectedStateShapeWarningMessage(state, finalReducers, action, unexpectedKeyCache)
+      const warningMessage = getUnexpectedStateShapeWarningMessage(state, finalReducers, action, unexpectedKeyCache)
       if (warningMessage) {
         warning(warningMessage)
       }
     }
 
-    var hasChanged = false
-    var nextState = {}
-    for (var i = 0; i < finalReducerKeys.length; i++) {
-      var key = finalReducerKeys[i]
-      var reducer = finalReducers[key]
-      var previousStateForKey = state[key]
-      var nextStateForKey = reducer(previousStateForKey, action)
+    let hasChanged = false
+    const nextState = {}
+    for (let i = 0; i < finalReducerKeys.length; i++) {
+      const key = finalReducerKeys[i]
+      const reducer = finalReducers[key]
+      const previousStateForKey = state[key]
+      const nextStateForKey = reducer(previousStateForKey, action)
       if (typeof nextStateForKey === 'undefined') {
-        var errorMessage = getUndefinedStateErrorMessage(key, action)
+        const errorMessage = getUndefinedStateErrorMessage(key, action)
         throw new Error(errorMessage)
       }
       nextState[key] = nextStateForKey

src/createStore.js

@@ -7,7 +7,7 @@ import $$observable from 'symbol-observable'
  * If the current state is undefined, you must return the initial state.
  * Do not reference these action types directly in your code.
  */
-export var ActionTypes = {
+export const ActionTypes = {
   INIT: '@@redux/INIT'
 }
 
@@ -54,11 +54,11 @@ export default function createStore(reducer, preloadedState, enhancer) {
     throw new Error('Expected the reducer to be a function.')
   }
 
-  var currentReducer = reducer
-  var currentState = preloadedState
-  var currentListeners = []
-  var nextListeners = currentListeners
-  var isDispatching = false
+  let currentReducer = reducer
+  let currentState = preloadedState
+  let currentListeners = []
+  let nextListeners = currentListeners
+  let isDispatching = false
 
   function ensureCanMutateNextListeners() {
     if (nextListeners === currentListeners) {
@@ -103,7 +103,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
       throw new Error('Expected listener to be a function.')
     }
 
-    var isSubscribed = true
+    let isSubscribed = true
 
     ensureCanMutateNextListeners()
     nextListeners.push(listener)
@@ -116,7 +116,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
       isSubscribed = false
 
       ensureCanMutateNextListeners()
-      var index = nextListeners.indexOf(listener)
+      const index = nextListeners.indexOf(listener)
       nextListeners.splice(index, 1)
     }
   }
@@ -172,9 +172,9 @@ export default function createStore(reducer, preloadedState, enhancer) {
       isDispatching = false
     }
 
-    var listeners = currentListeners = nextListeners
-    for (var i = 0; i < listeners.length; i++) {
-      var listener = listeners[i]
+    const listeners = currentListeners = nextListeners
+    for (let i = 0; i < listeners.length; i++) {
+      const listener = listeners[i]
       listener()
     }
 
@@ -207,7 +207,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
    * https://github.com/zenparsing/es-observable
    */
   function observable() {
-    var outerSubscribe = subscribe
+    const outerSubscribe = subscribe
     return {
       /**
        * The minimal observable subscription method.
@@ -229,7 +229,7 @@ export default function createStore(reducer, preloadedState, enhancer) {
         }
 
         observeState()
-        var unsubscribe = outerSubscribe(observeState)
+        const unsubscribe = outerSubscribe(observeState)
         return { unsubscribe }
       },