Proof of concept: enhancer overhaul

src/applyMiddleware.js

@@ -19,7 +19,7 @@ import compose from './compose'
 export default function applyMiddleware(...middlewares) {
   return (createStore) => (reducer, initialState, enhancer) => {
     var store = createStore(reducer, initialState, enhancer)
-    var dispatch
+    var dispatch = store.dispatch
     var chain = []
 
     var middlewareAPI = {

src/createStore.js

@@ -1,12 +1,11 @@
 import isPlainObject from 'lodash/isPlainObject'
-import warning from './utils/warning'
 import $$observable from 'symbol-observable'
 
 export var ActionTypes = {
   INIT: '@@redux/INIT'
 }
 
-function createBasicStore(reducer, initialState, onChange) {
+function createStoreBase(reducer, initialState, onChange) {
   var currentState = initialState
   var isDispatching = false
 
@@ -30,58 +29,70 @@ function createBasicStore(reducer, initialState, onChange) {
     if (isDispatching) {
       throw new Error('Reducers may not dispatch actions.')
     }
+
     try {
       isDispatching = true
       currentState = reducer(currentState, action)
     } finally {
       isDispatching = false
     }
+
     onChange()
     return action
   }
 
   return {
     dispatch,
-    getState,
+    getState
   }
 }
 
-export default function createEnhancedStore(reducer, initialState, enhancer) {
+export default function createStore(reducer, initialState, enhancer) {
   if (typeof reducer !== 'function') {
     throw new Error('Expected the reducer to be a function.')
   }
   if (typeof initialState === 'function' && typeof enhancer === 'undefined') {
     enhancer = initialState
     initialState = undefined
   }
-  var createStore = createBasicStore
-  if (typeof enhancer !== 'undefined') {
-    if (typeof enhancer !== 'function') {
-      throw new Error('Expected the enhancer to be a function.')
-    }
-    createStore = enhancer(createBasicStore)
+  if (typeof enhancer !== 'undefined' && typeof enhancer !== 'function') {
+    throw new Error('Expected the enhancer to be a function.')
   }
 
-  var store
+  enhancer = enhancer || (x => x)
+  var createFinalStoreBase = enhancer(createStoreBase)
+
+  var storeBase
   var currentListeners = []
   var nextListeners = currentListeners
 
+  function onChange() {
+    var listeners = currentListeners = nextListeners
+    for (var i = 0; i < listeners.length; i++) {
+      listeners[i]()
+    }
+  }
+
   function ensureCanMutateNextListeners() {
     if (nextListeners === currentListeners) {
       nextListeners = currentListeners.slice()
     }
   }
+
   function subscribe(listener) {
     if (typeof listener !== 'function') {
       throw new Error('Expected listener to be a function.')
     }
+
     var isSubscribed = true
     ensureCanMutateNextListeners()
     nextListeners.push(listener)
+
     return function unsubscribe() {
       if (!isSubscribed) {
         return
       }
+
       isSubscribed = false
       ensureCanMutateNextListeners()
       var index = nextListeners.indexOf(listener)
@@ -90,18 +101,21 @@ export default function createEnhancedStore(reducer, initialState, enhancer) {
   }
 
   function dispatch(action) {
-    return store.dispatch(action)
+    return storeBase.dispatch(action)
   }
 
-  function onChange() {
-    var listeners = currentListeners = nextListeners
-    for (var i = 0; i < listeners.length; i++) {
-      listeners[i]()
-    }
+  function getState() {
+    return storeBase.getState()
   }
 
-  function getState() {
-    return store.getState()
+  function replaceReducer(nextReducer) {
+    if (typeof nextReducer !== 'function') {
+      throw new Error('Expected the nextReducer to be a function.')
+    }
+
+    var nextInitialState = storeBase ? getState() : initialState
+    storeBase = createFinalStoreBase(nextReducer, nextInitialState, onChange)
+    dispatch({ type: ActionTypes.INIT })
   }
 
   function observable() {
@@ -126,15 +140,6 @@ export default function createEnhancedStore(reducer, initialState, enhancer) {
     }
   }
 
-  function replaceReducer(nextReducer) {
-    if (typeof nextReducer !== 'function') {
-      throw new Error('Expected the nextReducer to be a function.')
-    }
-
-    store = createStore(nextReducer, store ? getState() : initialState, onChange)
-    dispatch({ type: ActionTypes.INIT })
-  }
-
   replaceReducer(reducer)
 
   return {
@@ -144,4 +149,4 @@ export default function createEnhancedStore(reducer, initialState, enhancer) {
     replaceReducer,
     [$$observable]: observable
   }
-}
+}