假設我們有個 UI，在按鈕被按下時從遠端伺服器抓取一些使用者資料。（為了簡潔，我們將只顯示觸發行為的程式碼。）

class UserComponent extends React.Component {
  ...
  onSomeButtonClicked() {
    const { userId, dispatch } = this.props
    dispatch({type: 'USER_FETCH_REQUESTED', payload: {userId}})
  }
  ...
}

此元件會送出一個純物件行為到儲存。我們將建立一個 Saga，觀察所有 USER_FETCH_REQUESTED 行為，並觸發一個 API 呼叫以抓取使用者資料。

import { call, put, takeEvery, takeLatest } from 'redux-saga/effects'
import Api from '...'

// Worker saga will be fired on USER_FETCH_REQUESTED actions
function* fetchUser(action) {
   try {
      const user = yield call(Api.fetchUser, action.payload.userId);
      yield put({type: "USER_FETCH_SUCCEEDED", user: user});
   } catch (e) {
      yield put({type: "USER_FETCH_FAILED", message: e.message});
   }
}

// Starts fetchUser on each dispatched USER_FETCH_REQUESTED action
// Allows concurrent fetches of user
function* mySaga() {
  yield takeEvery("USER_FETCH_REQUESTED", fetchUser);
}

為執行我們的 Saga，我們必須使用 redux-saga 中介軟體將其連線到 Redux 儲存。

import { createStore, applyMiddleware } from 'redux'
import createSagaMiddleware from 'redux-saga'

import reducer from './reducers'
import mySaga from './sagas'

// Create the saga middleware
const sagaMiddleware = createSagaMiddleware()
// Mount it on the Store
const store = createStore(
  reducer,
  applyMiddleware(sagaMiddleware)
)

// Then run the saga
sagaMiddleware.run(mySaga)

// Render the application

這是新版的執行 saga，使用來自「 reduxjs/toolkit」的「configureStore」取代來自「 Redux」的「createStore」

import { configureStore } from '@reduxjs/toolkit'
import createSagaMiddleware from 'redux-saga'

import reducer from './reducers'
import mySaga from './sagas'

// Create the saga middleware
const sagaMiddleware = createSagaMiddleware()
const middleware = [sagaMiddleware]
// Mount it on the Store
const store = configureStore({
  reducer,
  middleware: (getDefaultMiddleware) =>
      getDefaultMiddleware().concat(middleware),
})

// Then run the saga
sagaMiddleware.run(mySaga)

// Render the application