Why You Should Use Redux Saga

We often use the Redux technology in our work. Not everyone is familiar with it. And some people don’t even know what it is about. Well, I’ll try to explain to you shortly what it is and why it is so interesting to us.

A pleasant surprise awaits those who read until the end of the article! Interested? Let’s go then!

Redux became the de facto standard as a data management technology for ReactJS applications. It is a convenient and easy method of structuring data in an application and displaying it on the client. Yet we hit a certain problem here. There is no place for side effects in the Redux scheme of work. As in the context of this article, only network requests are seen as side effects. Middleware can solve this problem.

Can Redux offer its own solution?

Two of the most common ways of dealing with side effects in Redux apps today are thunks and sagas.

Most people will ask, what are thunks and sagas? And how can they help?

The majority of projects use Redux Thunk to organize side effects. In principle, it gives a good result: it’s easy to read and test the code (but you still need to mock network requests). But it all is fair as far as the logic of your action creators (or thunks) is simple. Unfortunately, for more than a few functions the code becomes harder to read, which makes it even more difficult to test.

In this situation, Redux Saga comes to the rescue. Redux Saga is an alternative approach to the organization of side effects. Instead of dispatching functions processed by Redux Thunk you create saga and write all the logic of event stream processing. Unlike thunks that are carried out when you dispatch them, sagas run in the background right after the app is launched. Sagas observe all actions that the store dispatches and decide what to do with them.

At this point, we can allocate three key benefits of sagas:

Simplicity in organizing difficult side effects sequences
Declarative style
Simplicity of testing

So how can the saga be put into practice?

Let’s review an example of a simple saga which sends a network request.

function* request(action) {
   const response = yield call(api.method, action.payload)
   if (response.token) {
     yield put({type: ‘API_CALL_SUCCESS’, payload: response.token});
   } else {
     yield put({type: ‘API_CALL_FAIL’})
   }
}

function* mySaga() {
   takeEvery(‘API_CALL’, request)
}

Everything is quite simple and clear here. Our saga (which is the generator) expects some action, and after receiving it runs the handler function.

Is it possible to simplify the code more? Of course!

To make this code clearer and simpler, it is enough to improve it a little bit:

function* mySaga() {
   while ( true ) {
   yield take(‘API_CALL’);
   const response = yield call(api.method, action.payload)
   if (response.token) {
     yield put({type: ‘API_CALL_SUCCESS’, payload: response.token});
   } else {
     yield put({type: ‘API_CALL_FAIL’})
   }
}

In this example, we have launched an endless loop in this saga. As a result, the saga stops at the instructions “yield take ( ‘API_CALL’)” and waits for the desired action.

Special functions (effects) control sagas. In fact, these functions simply give a description of the desired call. For example, the call effect returns an object with reference to the desired function or a generator with parameters that it needs to be called with.

Since all calls in the saga are indirect (through effects), it’s easy to test them.

We can test our saga in this way:

if(‘should handle API_CALL type and perform api.method’, () => {
   const saga = mySaga();
   let next = saga.next();
   expect(next.value).toEqual(take(‘API_CALL’}));
   next = saga.next({type: ‘API_CALL’, payload: 1});
   expect(next.value).toEqual(call(api.method, {payload: 1}));
   next = saga.next({token: 1});
   expect(next.value).toEqual(put({type: ‘API_CALL_SUCCESS’}, payload: 1}))
});

Thus, Redux Saga allows you to write a complex sequence of synchronous and asynchronous events in a clear and declarative style without callbacks.

Well, in the end, I would like to share a useful link with you. It’s for those who are not left indifferent to the info above and who want to understand this topic in more detail here.