Redux 源码自己写了一遍
2024-09-19 22:37:33
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<meta http-equiv="content-type" content="text/html; charset=utf-8">
<title>Test</title>
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<script type='text/javascript'>
// var f = function( ...arg ){
// arg 是个数组
// ...arg 是传递进来的原封不动的值
// } // const reducer = function(state, action){
// if(!state){
// state = initialState;
// }
// let nextState = _.deepClone(state); // switch(action.type){
// case 'ADD_TODO':
// nextState.todos.push( action.payload );
// break;
// case 'INCREASE':
// nextState.counter = nextState.counter++;
// break;
// default:
// break;
// } // return nextState;
// } /*** compose ***/
// compose(func3, func2, func1)(0);
// 相当于写了 func3( func2( func1(0) ) )
const compose = function( ...funcs ) {
// 若没有传递参数, 则直接返还1个函数
if ( funcs.length === 0 ) {
return arg => arg;
} // 若只有1个参数, 则直接返还这个函数
if ( funcs.length === 1 ) {
return funcs[0];
} // 取出最后1个函数 当作 reduceRight的第2个参数
const last = funcs[funcs.length - 1];
// 取除了最后一个函数以外的函数数组
const rest = funcs.slice(0, -1);
// 所传递进来的参数 都当作 最后1个函数的参数
return (...args) => rest.reduceRight((composed, f) => f(composed), last(...args))
} /*** combineReducers ***/
const combineReducers = function(obj){
return function(state, action){
// nextState 为返回的新 state
let nextState = {};
for(var item in obj){
// obj[item] 为item 对应的reducer
/*
state[item] 的意思是 state 对应与 item 上的值,
比如 state 为 { counter: 0}, state[item]的值就为 0
*/
nextState[item] = obj[item]( state[item], action );
}
return nextState;
}
} /*** bindActionCreators ***/
const bindActionCreators = (obj, dispatch) => {
let objNew = {};
for(let i in obj){
// item 为创建 action 的函数
let item = obj[i];
objNew[i] = (...args) => {
dispatch( item(...args) );
}
}
return objNew;
} /*** applyMiddleware ***/
// 传入所有的中间件
const applyMiddleware = (...middlewares) => {
// 可以传入 createStore 作为参数
return (createStore) => {
// 这一步已经生成了 增强版本的 createStore
return (reducer, initialState, enhancer) => { let store = createStore(reducer, initialState, enhancer); // 这一步原来的写法是
// let chain = middlewares.map( middleware => middleware(store) );
// 源代码里是 从新创建了一个store
let storeNew = {
getState: store.getState,
dispatch: (action) => dispatch(action)
}
let chain = middlewares.map( middleware => middleware(storeNew) ); // 只有最后1个函数的传入了 store.dispatch 当作 dispatch,
// 其它函数都是最后1个函数的返回值当作 dispatch
const dispatch = compose(...chain)(store.dispatch); /*
最早本来想下面那样写,
这个结果是所有中间件的 dispatch 都为 store.dispach let chain = [...middlewares].map( (item) => {
return item(store)(store.dispatch);
} ); const dispatch = (action) => {
compose(...chain)(action);
}; 打印的结果为: 3 dispatch before
3 dispatch after
2 dispatch before
2 dispatch after
1 dispatch before
1 dispatch after */ return {
getState: store.getState,
subscribe: store.subscribe,
replaceReducer: store.replaceReducer,
dispatch: dispatch
}
}
}
} /*** createStore ***/
const createStore = function(reducer, initialState, enhancer){
if( typeof enhancer === "function"){
return enhancer(createStore)(reducer, initialState);
} let state = initialState;
// 操作的 listeners
let listeners = [];
let listenersCache = listeners; // 但凡 listeners 有变化, 比如push了 或者删除了, 都提前执行下 ensure
const ensure = function(){
// 若相等, 则拷贝一个新的 listeners
if( listeners == listenersCache ){
listeners = listenersCache.slice();
}
} const getState = function(){
return state;
} const dispatch = function(action){
state = reducer(state, action); // 为了让 ensure 执行成功
listenersCache = listeners;
let len = listenersCache.length;
for(let i = 0; i < len; i++){
listenersCache[i]();
} return action;
} const subscribe = listener => {
ensure();
listeners.push(listener); return function(){
ensure();
listeners = listeners.filter(function(item, i){
return item != listener;
});
} } dispatch({});
return {
dispatch: dispatch,
getState: getState,
subscribe: subscribe
}
} const initialState = {
counter: 0,
todos: []
} const counterReducer = function(counter = 0, action){
switch(action.type){
case 'INCREASE':
console.log('Reducer increase');
return counter = counter + 1;
default:
return counter;
}
} const todosReducer = function(todos = [], action){
switch(action.type){
case 'ADD_TODO':
return [...todos, action.payload];
default:
return todos;
}
} const rootReducer = combineReducers({
counter: counterReducer,
todos: todosReducer
}); const actionAdd = (n) => {
return {type: n}
} const store = createStore(rootReducer, initialState); const actionCreate = bindActionCreators(
{actionAdd: actionAdd},
store.dispatch
); store.subscribe(function(){
console.log( store.getState() );
}); store.dispatch( actionAdd('INCREASE') );
actionCreate.actionAdd('INCREASE');
store.dispatch({type: 'ADD_TODO', payload: 'hello world'}); console.log(' ---------- 分割线 ---------- '); // 中间件 1
// 根据源代码 middlewareAPI 是一个新的对象, 类似 store
// 只有store 里的dispatch 和 getState方法
const middleware1 = ( middlewareAPI ) => {
return (dispatch) => {
return (action) => {
console.log( '1 dispatch before' ); // 这个 dispatch 其实是 middleware2 里的函数 (action) => {...}
let actionReturn = dispatch(action); console.log( '1 dispatch after' );
return actionReturn;
}
}
}; const middleware2 = ( middlewareAPI ) => {
return (dispatch) => {
return (action) => {
console.log( '2 dispatch before' ); // 这个 dispatch 其实是 middleware3 里的函数 (action) => {...}
let actionReturn = dispatch(action); console.log( '2 dispatch after' );
return actionReturn;
}
}
}; const middleware3 = ( middlewareAPI ) => {
return (dispatch) => {
return (action) => {
console.log( '3 dispatch before' ); // 这个 dispatch 才是 store.dispatch, 最终只有这里调用 reducer 更新
let actionReturn = dispatch(action); console.log( '3 dispatch after' );
return actionReturn;
}
}
}; let enhancedCreateStore = applyMiddleware(middleware1, middleware2, middleware3)(createStore);
let storeEnhance = enhancedCreateStore(rootReducer, initialState); /*
最后的打印结果是: 1 dispatch before
2 dispatch before
3 dispatch before
Reducer increase
3 dispatch after
2 dispatch after
1 dispatch after
*/
storeEnhance.dispatch({type: 'INCREASE'}); </script>
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