Cancel Properly HTTP Requests in React Hooks and avoid Memory Leaks

Hello guys !

Today, let's take a look at cancelling a web request with fetch and Abort Controller in React Hooks!

When we work with Fetch to manage data, we sometimes want to cancel the request (e.g. when we leave the current page, when we leave a modal, ...).

In the example below , we fetch the data to display when switching route. But, we leave the route/page before the fetch is completed.

We just saw a memory leak in action! Lets see why this error occurred, and what it exactly means.

WHY A MEMORY LEAK?: We have a component that performs an asynchronous fetch(url) task, then updates the state of the component to display the elements, BUT we unmount the component before the request is even completed. The state of the unmounted component is updated (e.g. setUsers, setState), which follows a memory leak.

Let's use the new AbortController API !

Abort Controller allows you to subscribe to one or more Web Requests with the ability to cancel them.

Basics of AbortController

First of all, let's create a new AbortController object instance.

Now, we can access to controller.signal.

"The signal read-only property of the AbortController interface returns an AbortSignal object instance, which can be used to communicate with/abort a DOM request as desired." MDN Source

Let's see how to use it

And finally, if we want to cancel the current request, just call abort(). Also, you can get controller.signal.aborted which is a Boolean that indicates whether the request(s) the signal is communicating with is/are aborted (true) or not (false).

Note: When abort() is called, the fetch() promise rejects with a DOMException named AbortError.

Yeah, you just learned how to cancel a Web Request natively!

Let's do this with React Hooks !

BEFORE

Below is an example of a component that retrieves data in order to display them:

If I leave the page too fast and the request is not finished: MEMORY LEAK

AFTER

So let's useEffect to subscribe to our fetch request and to avoid memory leaks. We use the clean method of useEffect for calling abort() when our component unmount.

Now, no more memory leaks!

As always, feel free to reach out to me!

You can check this demo on abort-with-react-hooks.vercel.app.
Also, here the source code of this article in this gist.

Cheers

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