Asynchronous api calls with redux-saga

Question

I am following redux-saga documentation on helpers, and so far it seems pretty straight forward, however I stumbled upon an issue when it comes to performing an api call (as you will see link to the docs points to such example)

There is a part Api.fetchUser that is not explained, thus I don't quiet understand if that is something we need to handle with libraries like axios or superagent? or is that something else. And are saga effects like call, put etc.. equivalents of get, post? if so, why are they named that way? Essentially I am trying to figure out a correct way to perform a simple post call to my api at url example.com/sessions and pass it data like { email: 'email', password: 'password' }

1ven · Accepted Answer · 2016-08-05T15:14:59.317

Api.fetchUser is a function, where should be performed api ajax call and it should return promise.

In your case, this promise should resolve user data variable.

For example:

// services/api.js
export function fetchUser(userId) {
  // `axios` function returns promise, you can use any ajax lib, which can
  // return promise, or wrap in promise ajax call
  return axios.get('/api/user/' + userId);
};

Then is sagas:

function* fetchUserSaga(action) {
  // `call` function accepts rest arguments, which will be passed to `api.fetchUser` function.
  // Instructing middleware to call promise, it resolved value will be assigned to `userData` variable
  const userData = yield call(api.fetchUser, action.userId);
  // Instructing middleware to dispatch corresponding action.
  yield put({
    type: 'FETCH_USER_SUCCESS',
    userData
  });
}

call, put are effects creators functions. They not have something familiar with GET or POST requests.

call function is used to create effect description, which instructs middleware to call the promise. put function creates effect, in which instructs middleware to dispatch an action to the store.

Remember errorhandeling try{ const userData= .....yield... }catch (e) { yield put({ type: 'FETCH_USER_FAILED' }); } — Kasper Halvas Jensen, Jul 04 '17 at 08:24

score 6 · Answer 2 · answered Aug 05 '16 at 15:11

Things like call, put, take, race are effects creator functions. The Api.fetchUser is a placeholder for your own function that handles API requests.

Here’s a full example of a loginSaga:

export function* loginUserSaga() {
  while (true) {
    const watcher = yield race({
      loginUser: take(USER_LOGIN),
      stop: take(LOCATION_CHANGE),
    });

    if (watcher.stop) break;

    const {loginUser} = watcher || {};
    const {username, password} = loginUser || {};
    const data = {username, password};

    const login = yield call(SessionService.login, data);

    if (login.err === undefined || login.err === null && login.response) {
      yield put(loginSuccess(login.response));
    } else {
      yield put(loginError({message: 'Invalid credentials. Please try again.'}));
    }
  }
}

In this snippet, the SessionService is a class that implements a login method which handles the HTTP request to the API. The redux-saga call will call this method and apply the data parameter to it. In the snippet above, we can then evaluate the result of the call and dispatch loginSuccess or loginError actions accordingly using put.

A side note: The snippet above is a loginSaga that continuously listens for the USER_LOGIN event, but breaks when a LOCATION_CHANGE happens. This is thanks to the race effect creator.

Asynchronous api calls with redux-saga

2 Answers2