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Getting started

Install

$ npm install redux-saga

or

$ yarn add redux-saga

Alternatively, you may use the provided UMD builds directly in the <script> tag of an HTML page. See this section.

Usage Example

Suppose we have a UI to fetch some user data from a remote server when a button is clicked. (For brevity, we'll just show the action triggering code.)

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

The Component dispatches a plain Object action to the Store. We'll create a Saga that watches for all USER_FETCH_REQUESTED actions and triggers an API call to fetch the user data.

sagas.js

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);
}

/*
  Alternatively you may use takeLatest.

  Does not allow concurrent fetches of user. If "USER_FETCH_REQUESTED" gets
  dispatched while a fetch is already pending, that pending fetch is cancelled
  and only the latest one will be run.
*/
function* mySaga() {
  yield takeLatest("USER_FETCH_REQUESTED", fetchUser);
}

export default mySaga;

To run our Saga, we'll have to connect it to the Redux Store using the redux-saga middleware.

main.js

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

Using UMD build in the browser

There is also a UMD build of redux-saga available in the dist/ folder. When using the umd build redux-saga is available as ReduxSaga in the window object. This enables you to create Saga middleware without using ES6 import syntax like this:

var sagaMiddleware = ReduxSaga.default()

The UMD version is useful if you don't use Webpack or Browserify. You can access it directly from unpkg.

The following builds are available:

Important!
If the browser you are targeting doesn't support ES2015 generators, you must transpile them (i.e., with babel plugin) and provide a valid runtime, such as the one here. The runtime must be imported before redux-saga:

import 'regenerator-runtime/runtime'
// then
import sagaMiddleware from 'redux-saga'