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如何进行Redux的源码解析，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
预热
redux 函数内部包含了大量柯里化函数以及代码组合思想
柯里化函数(curry)
通俗的来讲，可以用一句话概括柯里化函数：返回函数的函数
// example const funcA = (a) => { return const funcB = (b) => { return a + b } };上述的funcA函数接收一个参数，并返回同样接收一个参数的funcB函数。
柯里化函数有什么好处呢?
避免了给一个函数传入大量的参数--我们可以通过柯里化来构建类似上例的函数嵌套，将参数的代入分离开，更有利于调试
降低耦合度和代码冗余，便于复用
举个栗子：
// 已知listA, listB两个Array，都由int组成，需要筛选出两个Array的交集 const listA = [1, 2, 3, 4, 5]; const listB = [2, 3, 4]; const checkIfDataExist = (list) => { return (target) => { return list.some(value => value === target) }; }; // 调用一次checkIfDataExist函数，并将listA作为参数传入，来构建一个新的函数。 // 而新函数的作用则是：检查传入的参数是否存在于listA里 const ifDataExist = checkIfDataExist(listA); // 使用新函数来对listB里的每一个元素进行筛选 const intersectionList = listB.filter(value => ifDataExist(value)); console.log(intersectionList); // [2, 3, 4]代码组合(compose)
代码组合就像是数学中的结合律：
const compose = (f, g) => { return (x) => { return f(g(x)); }; }; // 还可以再简洁点 const compose = (f, g) => (x) => f(g(x));通过这样函数之间的组合，可以大大增加可读性，效果远大于嵌套一大堆的函数调用，并且我们可以随意更改函数的调用顺序
Redux
combineReducers
// 回顾一下combineReducers的使用格式 // 两个reducer const todos = (state = INIT.todos, action) => { // .... }; const filterStatus = (state = INIT.filterStatus, action) => { // ... }; const appReducer = combineReducers({ todos, filterStatus });还记得combineReducers的黑魔法吗?即：
传入的Object参数中，对象的key与value所代表的reducer function同名
各个reducer function的名称和需要传入该reducer的state参数同名
源码标注解读(省略部分)：
export default function combineReducers(reducers) { // ***次筛选，参数reducers为Object // 筛选掉reducers中不是function的键值对 var reducerKeys = Object.keys(reducers); var finalReducers = {} for (var i = 0; i < reducerKeys.length; i++) { var key = reducerKeys[i]; if (typeof reducers[key] === 'function') { finalReducers[key] = reducers[key] } } var finalReducerKeys = Object.keys(finalReducers) // 二次筛选，判断reducer中传入的值是否合法（!== undefined） // 获取筛选完之后的所有key var sanityError try { // assertReducerSanity函数用于遍历finalReducers中的reducer，检查传入reducer的state是否合法 assertReducerSanity(finalReducers) } catch (e) { sanityError = e } // 返回一个function。该方法接收state和action作为参数 return function combination(state = {}, action) { // 如果之前的判断reducers中有不法值，则抛出错误 if (sanityError) { throw sanityError } // 如果不是production环境则抛出warning if (process.env.NODE_ENV !== 'production') { var warningMessage = getUnexpectedStateShapeWarningMessage(state, finalReducers, action) if (warningMessage) { warning(warningMessage) } } var hasChanged = false var nextState = {} // 遍历所有的key和reducer，分别将reducer对应的key所代表的state，代入到reducer中进行函数调用 for (var i = 0; i < finalReducerKeys.length; i++) { var key = finalReducerKeys[i] var reducer = finalReducers[key] // 这也就是为什么说combineReducers黑魔法--要求传入的Object参数中，reducer function的名称和要和state同名的原因 var previousStateForKey = state[key] var nextStateForKey = reducer(previousStateForKey, action) // 如果reducer返回undefined则抛出错误 if (typeof nextStateForKey === 'undefined') { var errorMessage = getUndefinedStateErrorMessage(key, action) throw new Error(errorMessage) } // 将reducer返回的值填入nextState nextState[key] = nextStateForKey // 如果任一state有更新则hasChanged为true hasChanged = hasChanged || nextStateForKey !== previousStateForKey } return hasChanged ? nextState : state } } // 检查传入reducer的state是否合法 function assertReducerSanity(reducers) { Object.keys(reducers).forEach(key => { var reducer = reducers[key] // 遍历全部reducer，并给它传入(undefined, action) // 当***个参数传入undefined时，则为各个reducer定义的默认参数 var initialState = reducer(undefined, { type: ActionTypes.INIT }) // ActionTypes.INIT几乎不会被定义，所以会通过switch的default返回reducer的默认参数。如果没有指定默认参数，则返回undefined，抛出错误 if (typeof initialState === 'undefined') { throw new Error( `Reducer "${key}" returned undefined during initialization. ` + `If the state passed to the reducer is undefined, you must ` + `explicitly return the initial state. The initial state may ` + `not be undefined.` ) } var type = '@@redux/PROBE_UNKNOWN_ACTION_' + Math.random().toString(36).substring(7).split('').join('.') if (typeof reducer(undefined, { type }) === 'undefined') { throw new Error( `Reducer "${key}" returned undefined when probed with a random type. ` + `Don't try to handle ${ActionTypes.INIT} or other actions in "redux/*" ` + `namespace. They are considered private. Instead, you must return the ` + `current state for any unknown actions, unless it is undefined, ` + `in which case you must return the initial state, regardless of the ` + `action type. The initial state may not be undefined.` ) } }) }createStore
// 回顾下使用方法 const store = createStore(reducers, state, enhance);
源码标注解读(省略部分)：
// 对于未知的action.type，reducer必须返回默认的参数state。这个ActionTypes.INIT就可以用来监测当reducer传入未知type的action时，返回的state是否合法 export var ActionTypes = { INIT: '@@redux/INIT' } export default function createStore(reducer, initialState, enhancer) { // 检查你的state和enhance参数有没有传反 if (typeof initialState === 'function' && typeof enhancer === 'undefined') { enhancer = initialState initialState = undefined } // 如果有传入合法的enhance，则通过enhancer再调用一次createStore if (typeof enhancer !== 'undefined') { if (typeof enhancer !== 'function') { throw new Error('Expected the enhancer to be a function.') } return enhancer(createStore)(reducer, initialState) } if (typeof reducer !== 'function') { throw new Error('Expected the reducer to be a function.') } var currentReducer = reducer var currentState = initialState var currentListeners = [] var nextListeners = currentListeners var isDispatching = false // 是否正在分发事件 function ensureCanMutateNextListeners() { if (nextListeners === currentListeners) { nextListeners = currentListeners.slice() } } // 我们在action middleware中经常使用的getState()方法，返回当前state function getState() { return currentState } // 注册listener，同时返回一个取消事件注册的方法。当调用store.dispatch的时候调用listener 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 // 从nextListeners中去除掉当前listener ensureCanMutateNextListeners() var index = nextListeners.indexOf(listener) nextListeners.splice(index, 1) } } // dispatch方法接收的action是个对象，而不是方法。 // 这个对象实际上就是我们自定义action的返回值，因为dispatch的时候，已经调用过我们的自定义action了，比如 dispatch(addTodo()) function dispatch(action) { if (!isPlainObject(action)) { throw new Error( 'Actions must be plain objects. ' + 'Use custom middleware for async actions.' ) } if (typeof action.type === 'undefined') { throw new Error( 'Actions may not have an undefined "type" property. ' + 'Have you misspelled a constant?' ) } // 调用dispatch的时候只能一个个调用，通过dispatch判断调用的状态 if (isDispatching) { throw new Error('Reducers may not dispatch actions.') } try { isDispatching = true currentState = currentReducer(currentState, action) } finally { isDispatching = false } // 遍历调用各个linster var listeners = currentListeners = nextListeners for (var i = 0; i < listeners.length; i++) { listeners[i]() } return action } // Replaces the reducer currently used by the store to calculate the state. function replaceReducer(nextReducer) { if (typeof nextReducer !== 'function') { throw new Error('Expected the nextReducer to be a function.') } currentReducer = nextReducer dispatch({ type: ActionTypes.INIT }) } // 当create store的时候，reducer会接受一个type为ActionTypes.INIT的action，使reducer返回他们默认的state，这样可以快速的形成默认的state的结构 dispatch({ type: ActionTypes.INIT }) return { dispatch, subscribe, getState, replaceReducer } }thunkMiddleware
源码及其简单简直给跪...
// 返回以 dispatch 和 getState 作为参数的action export default function thunkMiddleware({ dispatch, getState }) { return next => action => { if (typeof action === 'function') { return action(dispatch, getState); } return next(action); }; }applyMiddleware
先复习下用法：
// usage import {createStore, applyMiddleware} from 'redux'; import thunkMiddleware from 'redux-thunk'; const store = createStore( reducers, state, applyMiddleware(thunkMiddleware) );applyMiddleware首先接收thunkMiddleware作为参数，两者组合成为一个新的函数(enhance)，之后在createStore内部，因为enhance的存在，将会变成返回enhancer(createStore)(reducer, initialState)
源码标注解读(省略部分)：
// 定义一个代码组合的方法 // 传入一些function作为参数，返回其链式调用的形态。例如， // compose(f, g, h) 最终返回 (...args) => f(g(h(...args))) export default function compose(...funcs) { if (funcs.length === 0) { return arg => arg } else { const last = funcs[funcs.length - 1] const rest = funcs.slice(0, -1) return (...args) => rest.reduceRight((composed, f) => f(composed), last(...args)) } } export default function applyMiddleware(...middlewares) { // 最终返回一个以createStore为参数的匿名函数 // 这个函数返回另一个以reducer, initialState, enhancer为参数的匿名函数 return (createStore) => (reducer, initialState, enhancer) => { var store = createStore(reducer, initialState, enhancer) var dispatch var chain = [] var middlewareAPI = { getState: store.getState, dispatch: (action) => dispatch(action) } // 每个 middleware 都以 middlewareAPI 作为参数进行注入，返回一个新的链。此时的返回值相当于调用 thunkMiddleware 返回的函数： (next) => (action) => {} ，接收一个next作为其参数 chain = middlewares.map(middleware => middleware(middlewareAPI)) // 并将链代入进 compose 组成一个函数的调用链 // compose(...chain) 返回形如(...args) => f(g(h(...args)))，f/g/h都是chain中的函数对象。 // 在目前只有 thunkMiddleware 作为 middlewares 参数的情况下，将返回 (next) => (action) => {} // 之后以 store.dispatch 作为参数进行注入 dispatch = compose(...chain)(store.dispatch) return { ...store, dispatch } } }一脸懵逼?没关系，来结合实际使用总结一下：
当我们搭配redux-thunk这个库的时候，在redux配合components时，通常这么写
import thunkMiddleware from 'redux-thunk'; import { createStore, applyMiddleware, combineReducer } from 'redux'; import * as reducers from './reducers.js'; const appReducer = combineReducer(reducers); const store = createStore(appReducer, initialState, applyMiddleware(thunkMiddleware));还记得当createStore收到的参数中有enhance时会怎么做吗?
// createStore.js if (typeof enhancer !== 'undefined') { if (typeof enhancer !== 'function') { throw new Error('Expected the enhancer to be a function.') } return enhancer(createStore)(reducer, initialState) }也就是说，会变成下面的情况
applyMiddleware(thunkMiddleware)(createStore)(reducer, initialState)
applyMiddleware(thunkMiddleware)
applyMiddleware接收thunkMiddleware作为参数，返回形如(createStore) => (reducer, initialState, enhancer) => {}的函数。
applyMiddleware(thunkMiddleware)(createStore)
以 createStore 作为参数，调用上一步返回的函数(reducer, initialState, enhancer) => {}
applyMiddleware(thunkMiddleware)(createStore)(reducer, initialState)
以(reducer, initialState)为参数进行调用。
在这个函数内部，thunkMiddleware被调用，其作用是监测type是function的action
因此，如果dispatch的action返回的是一个function，则证明是中间件，则将(dispatch, getState)作为参数代入其中，进行action 内部下一步的操作。否则的话，认为只是一个普通的action，将通过next(也就是dispatch)进一步分发。
也就是说，applyMiddleware(thunkMiddleware)作为enhance，最终起了这样的作用：
对dispatch调用的action(例如，dispatch(addNewTodo(todo)))进行检查，如果action在***次调用之后返回的是function，则将(dispatch, getState)作为参数注入到action返回的方法中，否则就正常对action进行分发，这样一来我们的中间件就完成喽~
因此，当action内部需要获取state，或者需要进行异步操作，在操作完成之后进行事件调用分发的话，我们就可以让action 返回一个以(dispatch, getState)为参数的function而不是通常的Object，enhance就会对其进行检测以便正确的处理。
bindActionCreator
这个方法感觉比较少见，我个人也很少用到
在传统写法下，当我们要把 state 和 action 注入到子组件中时，一般会这么做：
import { connect } from 'react-redux'; import {addTodo, deleteTodo} from './action.js'; class TodoComponect extends Component { render() { return ( <ChildComponent deleteTodo={this.props.deleteTodo} addTodo={this.props.addTodo} /> ) } } function mapStateToProps(state) { return { state } } function mapDispatchToProps(dispatch) { return { deleteTodo: (id) => { dispatch(deleteTodo(id)); }, addTodo: (todo) => { dispatch(addTodo(todo)); } } } export default connect(mapStateToProps, mapDispatchToProps)(TodoComponect);使用bindActionCreators可以把 action 转为同名 key 的对象，但使用 dispatch 把每个 action 包围起来调用
惟一使用 bindActionCreators 的场景是当你需要把 action creator 往下传到一个组件上，却不想让这个组件觉察到 Redux 的存在，而且不希望把 Redux store 或 dispatch 传给它。
// 在本组件内的应用 addTodo(todo) { let action = TodoActions.addTodo(todo); this.props.dispatch(action); } deleteTodo(id) { let action = TodoActions.deleteTodo(id); this.props.dispatch(action); } render() { let dispatch = this.props.dispatch; // 传递给子组件 let boundActionCreators = bindActionCreators(TodoActions, dispatch); return ( <ChildComponent {...boundActionCreators} /> ) } } function mapStateToProps(state) { return { state } } export default connect(mapStateToProps)(TodoComponect)bindActionCreator源码解析
function bindActionCreator(actionCreator, dispatch) { return (...args) => dispatch(actionCreator(...args)) } // bindActionCreators期待一个Object作为actionCreators传入，里面是 key: action export default function bindActionCreators(actionCreators, dispatch) { // 如果只是传入一个action，则通过bindActionCreator返回被绑定到dispatch的函数 if (typeof actionCreators === 'function') { return bindActionCreator(actionCreators, dispatch) } if (typeof actionCreators !== 'object' || actionCreators === null) { throw new Error( `bindActionCreators expected an object or a function, instead received ${actionCreators === null ? 'null' : typeof actionCreators}. ` + `Did you write "import ActionCreators from" instead of "import * as ActionCreators from"?` ) } // 遍历并通过bindActionCreator分发绑定至dispatch var keys = Object.keys(actionCreators) var boundActionCreators = {} for (var i = 0; i < keys.length; i++) { var key = keys[i] var actionCreator = actionCreators[key] if (typeof actionCreator === 'function') { boundActionCreators[key] = bindActionCreator(actionCreator, dispatch) } } return boundActionCreators }react-redux
Provider
export default class Provider extends Component { getChildContext() { // 将其声明为 context 的属性之一 return { store: this.store } } constructor(props, context) { super(props, context) // 接收 redux 的 store 作为 props this.store = props.store } render() { return Children.only(this.props.children) } } if (process.env.NODE_ENV !== 'production') { Provider.prototype.componentWillReceiveProps = function (nextProps) { const { store } = this const { store: nextStore } = nextProps if (store !== nextStore) { warnAboutReceivingStore() } } } Provider.propTypes = { store: storeShape.isRequired, children: PropTypes.element.isRequired } Provider.childContextTypes = { store: storeShape.isRequired }connect
传入mapStateToProps,mapDispatchToProps,mergeProps,options。
首先获取传入的参数，如果没有则以默认值代替
const defaultMapStateToProps = state => ({}) // eslint-disable-line no-unused-vars const defaultMapDispatchToProps = dispatch => ({ dispatch }) const { pure = true, withRef = false } = options之后，通过
const finalMergeProps = mergeProps || defaultMergeProps
选择合并stateProps,dispatchProps,parentProps的方式，默认的合并方式 defaultMergeProps 为：
const defaultMergeProps = (stateProps, dispatchProps, parentProps) => ({ ...parentProps, ...stateProps, ...dispatchProps })返回一个以 Component 作为参数的函数。在这个函数内部，生成了一个叫做Connect的 Component
// ... return function wrapWithConnect(WrappedComponent) { const connectDisplayName = `Connect(${getDisplayName(WrappedComponent)})` // 检查参数合法性 function checkStateShape(props, methodName) {} // 合并props function computeMergedProps(stateProps, dispatchProps, parentProps) { const mergedProps = finalMergeProps(stateProps, dispatchProps, parentProps) if (process.env.NODE_ENV !== 'production') { checkStateShape(mergedProps, 'mergeProps') } return mergedProps } // start of Connect class Connect extends Component { constructor(props, context) { super(props, context); this.store = props.store || context.store const storeState = this.store.getState() this.state = { storeState } this.clearCache() } computeStateProps(store, props) { // 调用configureFinalMapState，使用传入的mapStateToProps方法（或默认方法），将state map进props } configureFinalMapState(store, props) {} computeDispatchProps(store, props) { // 调用configureFinalMapDispatch，使用传入的mapDispatchToProps方法（或默认方法），将action使用dispatch封装map进props } configureFinalMapDispatch(store, props) {} // 判断是否更新props updateStatePropsIfNeeded() {} updateDispatchPropsIfNeeded() {} updateMergedPropsIfNeeded() {} componentDidMount() { // 内部调用this.store.subscribe(this.handleChange.bind(this)) this.trySubscribe() } handleChange() { const storeState = this.store.getState() const prevStoreState = this.state.storeState // 对数据进行监听，发送改变时调用 this.setState({ storeState }) } // 取消监听，清除缓存 componentWillUnmount() { this.tryUnsubscribe() this.clearCache() } render() { this.renderedElement = createElement(WrappedComponent, this.mergedProps ) return this.renderedElement } } // end of Connect Connect.displayName = connectDisplayName Connect.WrappedComponent = WrappedComponent Connect.contextTypes = { store: storeShape } Connect.propTypes = { store: storeShape } return hoistStatics(Connect, WrappedComponent) } // ...我们看见，在connect的***，返回了使用hoistStatics包装的Connect和WrappedComponent
hoistStatics是什么鬼?为什么使用它?
Copies non-react specific statics from a child component to a parent component. Similar to Object.assign, but with React static keywords blacklisted from being overridden.
也就是说，它类似于Object.assign，作用是将子组件中的 static 方法复制进父组件，但不会覆盖组件中的关键字方法(如 componentDidMount)
import hoistNonReactStatic from 'hoist-non-react-statics'; hoistNonReactStatic(targetComponent, sourceComponent);
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