1. redux-saga #

• redux-saga 是一个 redux 的中间件，而中间件的作用是为 redux 提供额外的功能。
• 在 reducers 中的所有操作都是同步的并且是纯粹的，即 reducer 都是纯函数，纯函数是指一个函数的返回结果只依赖于它的参数，并且在执行过程中不会对外部产生副作用，即给它传什么，就吐出什么。
• 但是在实际的应用开发中，我们希望做一些异步的（如Ajax请求）且不纯粹的操作（如改变外部的状态），这些在函数式编程范式中被称为“副作用”。

redux-saga 就是用来处理上述副作用（异步任务）的一个中间件。它是一个接收事件，并可能触发新事件的过程管理者，为你的应用管理复杂的流程。

2. redux-saga工作原理 #

• sages 采用 Generator 函数来 yield Effects（包含指令的文本对象）
• Generator 函数的作用是可以暂停执行，再次执行的时候从上次暂停的地方继续执行
• Effect 是一个简单的对象，该对象包含了一些给 middleware 解释执行的信息。
• 你可以通过使用 effects API 如 fork，call，take，put，cancel 等来创建 Effect。

3. redux-saga分类 #

• worker saga 做左右的工作，如调用API，进行异步请求，获取异步封装结果
• watcher saga 监听被dispatch的actions,当接受到action或者知道其被触发时，调用worker执行任务
• root saga 立即启动saga的唯一入口

3.1 saga #

const PUT = 'PUT';
function * gen(){
     yield {type:PUT,action:{type:"ADD"}};
     yield new Promise((resolve)=>setTimeout(resolve,1000));
     yield {type:PUT,action:{type:"MINUS"}};
}
function run(gen){
    let it = gen();
    function next(){
        let {done,value:effect} = it.next();
        if(!done){
            if(effect instanceof Promise){
                effect.then(()=>{
                    if(!done){
                        next();
                    }
                });
            }else{
                if(effect.type === PUT){
                    console.log('派发',effect.action);
                }
                if(!done){
                    next();
                }
            }
        }
    }
    next();
}
run(gen);

3.2 saga #

function * gen(){
    yield 1;
    yield 2;
    yield 3;
}
let it = gen();
console.log(it[Symbol.iterator]);
let r1 = it.next();
console.log(r1);
//let r2 = it.next();
//let r2 = it.throw();
let r2 = it.return();
console.log(r2);
let r3 = it.next();
console.log(r3);
let r4 = it.next();
console.log(r4);

3.3 once #

let EventEmitter = require('events');
let e = new EventEmitter();
e.once('click',(data)=>{
    console.log('clicked',data);
});
e.emit('click','data');
e.emit('click','data');

4. 计数器 #

4.1 index.js #

src/index.js

import React from 'react'
import ReactDOM from 'react-dom';
import Counter from './components/Counter';
import {Provider} from 'react-redux';
import store from './store';
ReactDOM.render(<Provider store={store}>
  <Counter/>
</Provider>,document.querySelector('#root'));

4.2 sagas.js #

src\store\sagas.js

import {put,take} from 'redux-saga/effects';
import * as types from './action-types';
function delay(ms) {
    return new Promise((resolve) => {
        setTimeout(resolve, ms);
    });
}
function * workerAdd(){
  yield delay(1000);
  yield put({type:actionTypes.ADD});
}
function * watcherAdd(){
  yield take(actionTypes.ASYNC_ADD);
  yield workerAdd();
}

export default function* rootSaga() {
  yield watcherAdd();
}

4.3 Counter.js #

src/components/Counter.js

import React,{Component} from 'react'
import {connect} from 'react-redux';
import actionCreators from '../store/actionCreators';
class Counter extends Component{
    render() {
        return (
            <div>
                <p>{this.props.number}</p>
                <button onClick={this.props.add}>+</button>
            </div>
      )
  }
}
export default connect(
    state => state,
    actionCreators
)(Counter);

4.4 index.js #

src/store/index.js

import {createStore, applyMiddleware} from 'redux';
import reducer from './reducer';
import createSagaMiddleware from 'redux-saga';
import rootSaga from './sagas';
let sagaMiddleware=createSagaMiddleware();
let store=applyMiddleware(sagaMiddleware)(createStore)(reducer);
sagaMiddleware.run(rootSaga);
window.store=store;
export default store;

4.5 actions.js #

src/store/actionCreators.js

import * as types from './action-types';
const actionCreators = {
    add() {
        return {type:types.ASYNC_ADD}
    }
}
export default  actionCreators

4.6 action-types.js #

src/store/action-types.js

export const ASYNC_ADD='ASYNC_ADD';
export const ADD='ADD';

4.7 reducer.js #

src/store/reducer.js

import * as types from './action-types';
export default function reducer(state={number:0},action) {
    switch(action.type){
        case types.ADD:
            return {number: state.number+1};
        default:
            return state;
    }
}

5. 实现take #

• runSaga.js

5.1 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';

5.2 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType}
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

5.3 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes'
export default function runSaga(env, saga) {
    let { eventEmitter, dispatch } = env;
    let it = typeof saga === 'function'?saga():saga;
    function next(value) {
        let {value:effect,done} = it.next(value);
        if (!done) {
            if(typeof effect[Symbol.iterator] === 'function'){
                runSaga(env,effect);
                next();//不会阻止当前saga继续向后走
            }else if (effect instanceof Promise) {
                effect.then(next);
            }else{
                switch (effect.type) {
                    case effectTypes.TAKE:
                        eventEmitter.once(effect.actionType,next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
                    default:
                        break;
               }
            }

        }
    }
    next();
}

5.4 index.js #

redux-saga/index.js

import EventEmitter from 'events';
import runSaga from './runSaga';
export default function createSagaMiddleware() {
    let eventEmitter = new EventEmitter();
    let boundRunSaga;
    function sagaMiddleware({getState,dispatch}) {
        boundRunSaga=runSaga.bind(null,{eventEmitter,dispatch,getState});
        return function (next) {
            return function (action) {
                const result = next(action);
                eventEmitter.emit(action.type, action);
                return result;
            }
        }
    }
    sagaMiddleware.run = (saga)=>boundRunSaga(saga);
    return sagaMiddleware;
}

6. 支持fork #

6.1 sagas.js #

+import { put, takeEvery } from '../redux-saga/effects';
import * as actionTypes from './action-types';
+export function* add() {
+    yield put({ type: actionTypes.ADD });
+}
+export default function* rootSaga() {
+   yield fork(add);
+}

6.2 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';
+export const FORK = 'FORK';

6.3 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

+export function fork(saga) {
+    return { type: effectTypes.FORK, saga };
+}

6.4 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes'
export default function runSaga(env, saga) {
    let { channel, dispatch } = env;
    let it = typeof saga == 'function' ? saga() : saga;
    function next(value) {
        let { value: effect, done } = it.next(value);
        if (!done) {
            if (typeof effect[Symbol.iterator] == 'function') {
                runSaga(env,effect);
                next();
            } else {
                switch (effect.type) {
                    case effectTypes.TAKE:
                        channel.take(effect.actionType, next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
+                    case effectTypes.FORK:
+                        runSaga(env,effect.saga);
+                        next();
+                        break;
                    default:
                        break;
                }
            }

        }
    }
    next();
}

7. 支持takeEvery #

• 一个 task 就像是一个在后台运行的进程，在基于redux-saga的应用程序中，可以同时运行多个task
• 通过 fork 函数来创建 task

7.1 sagas.js #

+import { put, takeEvery } from '../redux-saga/effects';
import * as actionTypes from './action-types';
export function* add() {
    yield put({ type: actionTypes.ADD });
}
export default function* rootSaga() {
+    yield takeEvery(actionTypes.ASYNC_ADD,add);
}

7.2 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

export function fork(saga) {
    return { type: effectTypes.FORK, saga };
}

+export function takeEvery(actionType, saga) {
+    function* takeEveryHelper() {
+        while (true) {
+            yield take(actionType);
+            yield fork(saga);
+        }
+    }
+    return fork(takeEveryHelper);
+}

8. 支持 call #

8.1 sagas.js #

src\store\sagas.js

+import { put, takeEvery,call } from '../redux-saga/effects';
import * as actionTypes from './action-types';
const delay = ms => new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve();
    }, ms);
});
export function* add() {
+    yield call(delay,1000);
    yield put({ type: actionTypes.ADD });
}
export default function* rootSaga() {
    yield takeEvery(actionTypes.ASYNC_ADD, add);
}

8.2 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';
export const FORK = 'FORK';
+export const CALL = 'CALL';

8.3 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

export function fork(saga) {
    return { type: effectTypes.FORK, saga };
}

export function takeEvery(pattern, saga) {
    function* takeEveryHelper() {
        while (true) {
            yield take(pattern);
            yield fork(saga);
        }
    }
    return fork(takeEveryHelper);
}
+export function call(fn, ...args) {
+    return { type: effectTypes.CALL, fn, args };
+}

8.4 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes'
export default function runSaga(env, saga) {
    let { channel, dispatch } = env;
    let it = typeof saga == 'function' ? saga() : saga;
    function next(value) {
        let { value: effect, done } = it.next(value);
        if (!done) {
            if (typeof effect[Symbol.iterator] == 'function') {
                runSaga(env,effect);
                next();
            }else if(effect.then){
                effect.then(next);
            } else {
                switch (effect.type) {
                    case effectTypes.TAKE:
                        channel.take(effect.actionType, next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
                    case effectTypes.FORK:
                        runSaga(env,effect.saga);
                        next();
                        break;
+                    case effectTypes.CALL:
+                        effect.fn(...effect.args).then(next);
+                        break;
                    default:
                        break;
                }
            }

        }
    }
    next();
}

9. 支持 cps #

9.1 sagas.js #

src\store\sagas.js

+import { put, takeEvery,call,cps} from '../redux-saga/effects';
import * as actionTypes from './action-types';
+const delay = (ms,callback)=>{
+    setTimeout(() => {
+        callback(null,'ok');
+    },ms);
+}
export function* add() {
+    let data = yield cps(delay,1000);
+    console.log(data);
    yield put({ type: actionTypes.ADD });
}
export default function* rootSaga() {
    yield takeEvery(actionTypes.ASYNC_ADD, add);
}

9.2 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';
export const FORK = 'FORK';
export const CALL = 'CALL';
+export const CPS = 'CPS';

9.3 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

export function fork(saga) {
    return { type: effectTypes.FORK, saga };
}

export function takeEvery(pattern, saga) {
    function* takeEveryHelper() {
        while (true) {
            yield take(pattern);
            yield fork(saga);
        }
    }
    return fork(takeEveryHelper);
}
export function call(fn, ...args) {
    return { type: effectTypes.CALL, fn, args };
}
+export function cps(fn, ...args) {
+    return { type: effectTypes.CPS, fn, args };
+}

9.4 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes'
export default function runSaga(env, saga) {
    let { channel, dispatch } = env;
    let it = typeof saga == 'function' ? saga() : saga;
+    function next(value,isErr) {
+        let result;
+        if (isErr) {
+            result = it.throw(value);
+          } else {
+            result = it.next(value);
+          }
+        let { value: effect, done } = result;
        if (!done) {
            if (typeof effect[Symbol.iterator] == 'function') {
                runSaga(env,effect);
                next();
            }else if(effect.then){
                effect.then(next);
            } else {
                switch (effect.type) {
                    case effectTypes.TAKE:
                        channel.take(effect.actionType, next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
                    case effectTypes.FORK:
                        runSaga(env,effect.saga);
                        next();
                        break;
                    case effectTypes.CALL:
                        effect.fn(...effect.args).then(next);
                        break;
+                    case effectTypes.CPS:
+                        effect.fn(...effect.args,(err,data)=>{
+                            if(err){
+                                next(err,true);
+                            }else{
+                                next(data);
+                            }
+                        });
+                        break;    
                    default:
                        break;
                }
            }

        }
    }
    next();
}

11. 支持all #

11.1 saga #

src\store\sagas.js

import { put, takeEvery, call, cps, take,all } from '../redux-saga/effects';
import * as actionTypes from './action-types';
+export function* add1() {
+    for (let i = 0; i < 1; i++) {
+        yield take(actionTypes.ASYNC_ADD);
+        yield put({ type: actionTypes.ADD });
+    }
+    console.log('add1 done ');
+    return 'add1Result';
+}
+export function* add2() {
+    for (let i = 0; i < 2; i++) {
+        yield take(actionTypes.ASYNC_ADD);
+        yield put({ type: actionTypes.ADD });
+    }
+    console.log('add2 done ');
+    return 'add2Result';
+}
export default function* rootSaga() {
+    let result = yield all([add1(), add2()]);
+    console.log('done', result);
}

11.2 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';
export const FORK = 'FORK';
export const CALL = 'CALL';
export const CPS = 'CPS';
export const ALL = 'ALL';

11.3 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

export function fork(saga) {
    return { type: effectTypes.FORK, saga };
}

export function takeEvery(pattern, saga) {
    function* takeEveryHelper() {
        while (true) {
            yield take(pattern);
            yield fork(saga);
        }
    }
    return fork(takeEveryHelper);
}
export function call(fn, ...args) {
    return { type: effectTypes.CALL, fn, args };
}
export function cps(fn, ...args) {
    return { type: effectTypes.CPS, fn, args };
}
+export function all(iterators) {
+    return { type: effectTypes.ALL, iterators };
+}

11.4 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes'
+export default function runSaga(env, saga,callback) {
    let { channel, dispatch } = env;
    let it = typeof saga == 'function' ? saga() : saga;
    function next(value, isErr) {
        let result;
        if (isErr) {
            result = it.throw(value);
        } else {
            result = it.next(value);
        }
        let { value: effect, done } = result;
        if (!done) {
            if (typeof effect[Symbol.iterator] == 'function') {
                runSaga(env, effect);
                next();
            } else if (effect.then) {
                effect.then(next);
            } else {
                switch (effect.type) {
                    case effectTypes.TAKE:
                        channel.take(effect.actionType, next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
                    case effectTypes.FORK:
                        runSaga(env, effect.saga);
                        next();
                        break;
                    case effectTypes.CALL:
                        effect.fn(...effect.args).then(next);
                        break;
                    case effectTypes.CPS:
                        effect.fn(...effect.args, (err, data) => {
                            if (err) {
                                next(err, true);
                            } else {
                                next(data);
                            }
                        });
                        break;
+                    case effectTypes.ALL:
+                        let {iterators}=effect;
+                        let result = [];
+                        let completeCount=0;
+                        iterators.forEach((iterator,index)=>runSaga(env,effect,(data)=>{
+                            result[index]=data;
+                            if(++completeCount === iterators.length)
+                                next(result);
+                        }));
+                        break;
                    default:
                        break;
                }
            }
        } else {
+            callback && callback(effect);
        }
    }
    next();
}

12. 取消任务 #

12.1 sagas.js #

src\store\sagas.js

+import { put, takeEvery, call, cps, all, take, cancel, fork, delay } from '../redux-saga/effects';
+import * as actionTypes from './action-types';
+export function* add() {
+    while (true) {
+        yield delay(1000);
+        yield put({ type: actionTypes.ADD });
+    }
+}
+export function* addWatcher() {
+    const task = yield fork(add);
+    console.log(task);
+    yield take(actionTypes.STOP_ADD);
+    yield cancel(task);
+}

+export default function* rootSaga() {
+    yield addWatcher();
+}

12.2 effectTypes.js #

src\redux-saga\effectTypes.js

export const TAKE = 'TAKE';
export const PUT = 'PUT';
export const FORK = 'FORK';
export const CALL = 'CALL';
export const CPS = 'CPS';
export const ALL = 'ALL';
+export const CANCEL = 'CANCEL';

12.3 effects.js #

src\redux-saga\effects.js

import * as effectTypes from './effectTypes'
export function take(actionType) {
    return { type: effectTypes.TAKE, actionType }
}

export function put(action) {
    return { type: effectTypes.PUT, action }
}

export function fork(saga) {
    return { type: effectTypes.FORK, saga };
}

export function takeEvery(pattern, saga) {
    function* takeEveryHelper() {
        while (true) {
            yield take(pattern);
            yield fork(saga);
        }
    }
    return fork(takeEveryHelper);
}
export function call(fn, ...args) {
    return { type: effectTypes.CALL, fn, args };
}
export function cps(fn, ...args) {
    return { type: effectTypes.CPS, fn, args };
}
export function all(effects) {
    return { type: effectTypes.ALL, effects };
}
+export function cancel(task) {
+    return { type: effectTypes.CANCEL, task };
+}

12.4 runSaga.js #

src\redux-saga\runSaga.js

import * as effectTypes from './effectTypes';
const CANCEL_TASK = 'CANCEL_TASK';
export default function runSaga(env, saga,callback) {
+    let task = {cancel:()=>next(TASK_CANCEL)};
    let { channel, dispatch } = env;
    let it = typeof saga == 'function' ? saga() : saga;
    function next(value, isErr) {
        let result;
        if (isErr) {
            result = it.throw(value);
+        }else if(value === TASK_CANCEL){
+            result = it.return(value);
        } else {
            result = it.next(value);
        }
        let { value: effect, done } = result;
        if (!done) {
            if (typeof effect[Symbol.iterator] == 'function') {
                runSaga(env, effect);
                next();
            } else if (effect.then) {
                effect.then(next);
            } else {
                switch (effect.type) {
                    case effectTypes.TAKE:
                        channel.take(effect.actionType, next);
                        break;
                    case effectTypes.PUT:
                        dispatch(effect.action);
                        next();
                        break;
                    case effectTypes.FORK:
+                        let forkTask = runSaga(env, effect.saga);
+                        next(forkTask);
                        break;
                    case effectTypes.CALL:
                        effect.fn(...effect.args).then(next);
                        break;
                    case effectTypes.CPS:
                        effect.fn(...effect.args, (err, data) => {
                            if (err) {
                                next(err, true);
                            } else {
                                next(data);
                            }
                        });
                        break;
                    case effectTypes.ALL:
                        let effects=effect.effects;
                        let result = [];
                        let complete=0;
                        effects.forEach((effect,index)=>runSaga(env,effect,(res)=>{
                            result[index]=res;
                            if(++complete === effects.length)
                                next(result);
                        }));
                        break;
+                    case effectTypes.CANCEL:
+                        effect.task.cancel();
+                        next();
+                        break;    
                    default:
                        break;
                }
            }
        } else {
            callback && callback(effect);
        }
    }
    next();
+    return task;
}

12.5 action-types.js #

src\store\action-types.js

export const ASYNC_ADD='ASYNC_ADD';
export const ADD='ADD';
+export const STOP='STOP';

12.6 Counter.js #

src\components\Counter.js

import React,{Component} from 'react'
import {connect} from 'react-redux';
import actions from '../store/actions';
class Counter extends Component{
    render() {
        return (
            <div>
                <p>{this.props.number}</p>
+                <button onClick={this.props.stop}>stop</button>
            </div>
      )
  }
}
export default connect(
    state => state,
    actions
)(Counter);

12.7 actions.js #

src\store\actions.js

import * as actionTypes from './action-types';
const actions = {
    add() {
        return { type: actionTypes.ASYNC_ADD }
    },
+    stop() {
+        return { type: actionTypes.STOP }
+    }
}
export default actions