How to cancel fetch on demand OR with timeout

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By default, the web fetch doesn’t have a timeout option. This means that a request will never be cancelled unless it's explicitly cancelled. So, how do we cancel a fetch request on demand? And how do we set a timeout for a fetch request? Taking it even further, how do we allow a user to cancel the fetch before the timeout is reached?

When I asked ChatGPT about the default timeout for fetch, here's what it said:

The fetch API in browsers does not have a built-in timeout mechanism. By default, a fetch request will run indefinitely until the server responds or the connection is closed by some network error. If you need to implement a timeout, you have to do it manually with setTimeout and abort the fetch using an AbortController. Here’s a quick example:

const controller = new AbortController()
const timeoutId = setTimeout(() => controller.abort(), 5000) // Set timeout to 5000 ms

fetch('https://example.com', { signal: controller.signal })
  .then((response) => response.json())
  .then((data) => console.log(data))
  .catch((error) => console.error('Fetch aborted:', error))
  .finally(() => clearTimeout(timeoutId))

This sets up a fetch request that will be aborted if it takes longer than 5000 milliseconds (5 seconds).

The above code seems alright, but it's a bit complicated. There's an easier way to do it—use AbortSignal.timeout.

try {
  const res = await fetch(url, { signal: AbortSignal.timeout(5000) })
  const result = await res.blob()
  // …
} catch (err) {
  if (err.name === 'TimeoutError') {
    console.error('Timeout: It took more than 5 seconds to get the result!')
  } else {
    // A network error, or some other problem.
    console.error(`Error: type: ${err.name}, message: ${err.message}`)
  }
}

Next, we want to allow the user to cancel the fetch manually. We can use the same AbortController to abort the fetch request. Here's the code:

import { useEffect, useRef } from 'react';

function MyComponent() {
  const abortControllerRef = useRef(new AbortController());

  useEffect(() => {
    const fetchData = async () => {
      const response = await fetch(someURL, { signal: abortControllerRef.current.signal });
      const data = await response.json();
      // Do something with data
    };
    fetchData();

    return () => {
      abortControllerRef.current.abort();
    };
  }, []);

  return (
    <button onClick={() => abortControllerRef.current.abort()}>Cancel</button>
  );
}

Finally, we want the fetch to be canceled if the user clicks the cancel button OR if the timeout is reached. Luckily, the platform provides us with a built-in way to achieve this using the AbortSignal.any:

import { useEffect, useRef } from 'react';

function MyComponent() {
  // in production, don't use multiple states like this. Check out my previous blog post.
  const [loading, setLoading] = useState(false)
  const [data, setData] = useState<any>(null)
  const [error, setError] = useState<any>(null)
  const abortControllerRef = useRef<AbortController | null>(null)

  useEffect(() => {
    let isCleandUp = false

    const abortController = new AbortController()
    abortControllerRef.current = abortController

    const fetchData = async () => {
      // reset the states
      setLoading(true)
      setError(null)
      setData(null)

      // @ts-ignore don't know why TS doesn't recognize any
      const combinedSignal = AbortSignal.any([
        abortController.signal,
        AbortSignal.timeout(1_000 * 5), // 5 seconds timeout
      ])
      const url = window.location.protocol + '//' + window.location.host
      const fetchURL = `${url}/experiments/fetch-abort-demo/api`
      try {
        const response = await fetch(fetchURL, {
          signal: combinedSignal,
        })
        const data = await response.json()

        if (!isCleandUp) {
          setData(data)
          setLoading(false)
          setError(null)
        }
      } catch (error: any) {
        if (!isCleandUp) {
          setLoading(false)

          if (error.name === 'TimeoutError') {
            setError('Timeout: It took more than 5 seconds to get the result!')
          }
          if (error.name === 'AbortError') {
            setError(`Fetch canceled by user`)
          }
        }
      }
    }

    fetchData()

    return () => {
      isCleandUp = true
      abortController.abort()
      abortControllerRef.current = null
    }
  }, [])

  return (
    <div>
      {data && !loading && !error ? <p>Data: {data.message}</p> : null}
      {error && !loading && !data ? <p>Error: {error}</p> : null}
      {loading ? (
        <button
          className="cursor-default rounded-md border border-black px-4 py-2"
          onClick={() => abortControllerRef.current?.abort()}
        >
          Loading. Will timeout in 5 seconds. Click to cancel now.
        </button>
      ) : null}
    </div>
  )
}

Check out the demo here. Note that as of this writing, the demo doesn't work in Safari, only in Chrome and Firefox, even though Safari is supposed to support AbortController.any since version 17.4.

By the way, I'm making a book about Pull Requests Best Practices. Check it out!

How to cancel fetch on demand OR with timeout

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