$ npm install --save redux-saga
//或者
$ yarn add redux-saga

{
 "297ee83e-4d15-4eb7-8106-e1e5e212933c": {
  "username": "Saga"
 }
}

import React from 'react';
import { USER_FETCH_REQUESTED } from '../../../actions/User';

export default class extends React.Component {

 constructor(props) {
  super(props);
  this.state = { userId: '297ee83e-4d15-4eb7-8106-e1e5e212933c' }
 }

 render() {
  const { userInfo = {}, dispatch } = this.props;
  return (
   <React.Fragment>
    <button onClick={() => {
     dispatch({ type: USER_FETCH_REQUESTED, payload: { userId: this.state.userId } });
    }}>Get User Info</button> <span>用户名： {userInfo.username}</span>
   </React.Fragment>
  );
 }
}

import { call, put, takeEvery } from 'redux-saga/effects'
import { fetchUserApi } from '../api/user';
import { USER_FETCH_REQUESTED, USER_FETCH_SUCCEEDED, USER_FETCH_FAILED } from '../actions/User';

function* fetchUser({ payload }) {
 try {
  const user = yield call(fetchUserApi, payload.userId);
  yield put({ type: USER_FETCH_SUCCEEDED, user });
 } catch (e) {
  yield put({ type: USER_FETCH_FAILED, message: e.message });
 }
}

const userSaga = function* () {
 yield takeEvery(USER_FETCH_REQUESTED, fetchUser);
}

export default userSaga;

import createSagaMiddleware from 'redux-saga';
import Sagas from '../sagas/index';

const sagaMiddleware = createSagaMiddleware()
const store = createStore(
 reducer,
 applyMiddleware(sagaMiddleware)
)
sagaMiddleware.run(Sagas)

import { USER_FETCH_SUCCEEDED } from '../actions/User';

const initialState = { user: {} };

export default (state = initialState, action) => {
 switch (action.type) {
  case USER_FETCH_SUCCEEDED:
   return { ...state, user: action.user };
  default:
   return state;
 }
}