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' }
Using Redux Saga to handle multiple async requestsInstead of invoking the asynchronous request directly, the method call will return only a plain object describing the operation. Redux Saga then takes care of the invocation and return the result to the generator. The same thing happens with the put method.
You can transpile async/await into generators, but you can't do the reverse. As a userland library, redux-saga can handle asynchronous behavior in ways that async/await doesn't.
The redux-saga middleware takes care of executing the function call and resuming the generator with the resolved response. This allows us to easily test the Generator outside the Redux environment. Because call is just a function which returns a plain Object.
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.
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.
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