redux-saga-example.js

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

// every time a FETCH_USER_INFO action is dipatched, the function fechtUserInfo will be called
function* watchFetchUserInfo() {
 yield takeEvery(FETCH_USER_INFO, fetchUserInfo);
}

function* fetchUserInfo (action) {
  try {
    // tell redux-saga => call this functions and once done put them in pictureResponse, infoResponse
    const [pictureResponse, infoResponse] = yield [
      call(fetch, `https://graph.facebook.com/${action.payload.userID}/picture?type=large&redirect=false`),
      call(fetch, `https://graph.facebook.com/v2.5/me?fields=email,name,friends&access_token=${action.payload.accessToken}`),
    ];

    // here both call are resolved
    
    // tell redux-saga => dipatch this actions in redux
    yield put(receiveProfilePicture(pictureResponse.json().data.url));
    yield put(receiveUserInformation(infoResponse.json());
              
    // here both actions have been dispatched and runned through reducers
    // you can do whatever you need, put to dispatch an action, call another func, etc
    
   } catch (e) {
      // here you can handle if either of the call failed
      yield put({type: "USER_FETCH_FAILED", message: e.message});
   }
}