[javascript] Fetch API request timeout?

I have a fetch-api POST request:

fetch(url, {
  method: 'POST',
  body: formData,
  credentials: 'include'
})

I want to know what is the default timeout for this? and how can we set it to a particular value like 3 seconds or indefinite seconds?

You can create a timeoutPromise wrapper

function timeoutPromise(timeout, err, promise) {
  return new Promise(function(resolve,reject) {
    promise.then(resolve,reject);
    setTimeout(reject.bind(null,err), timeout);
  });
}

You can then wrap any promise

timeoutPromise(100, new Error('Timed Out!'), fetch(...))
  .then(...)
  .catch(...)  

It won't actually cancel an underlying connection but will allow you to timeout a promise.
Reference

Using c-promise2 lib the cancellable fetch with timeout might look like this one (Live jsfiddle demo):

import CPromise from "c-promise2"; // npm package

function fetchWithTimeout(url, {timeout, ...fetchOptions}= {}) {
    return new CPromise((resolve, reject, {signal}) => {
        fetch(url, {...fetchOptions, signal}).then(resolve, reject)
    }, timeout)
}
        
const chain = fetchWithTimeout("https://run.mocky.io/v3/753aa609-65ae-4109-8f83-9cfe365290f0?mocky-delay=10s", {timeout: 5000})
    .then(request=> console.log('done'));
    
// chain.cancel(); - to abort the request before the timeout

This code as a npm package cp-fetch

EDIT: The fetch request will still be running in the background and will most likely log an error in your console.

Indeed the Promise.race approach is better.

See this link for reference Promise.race()

Race means that all Promises will run at the same time, and the race will stop as soon as one of the promises returns a value. Therefore, only one value will be returned. You could also pass a function to call if the fetch times out.

fetchWithTimeout(url, {
  method: 'POST',
  body: formData,
  credentials: 'include',
}, 5000, () => { /* do stuff here */ });

If this piques your interest, a possible implementation would be :

function fetchWithTimeout(url, options, delay, onTimeout) {
  const timer = new Promise((resolve) => {
    setTimeout(resolve, delay, {
      timeout: true,
    });
  });
  return Promise.race([
    fetch(url, options),
    timer
  ]).then(response => {
    if (response.timeout) {
      onTimeout();
    }
    return response;
  });
}

Using a promise race solution will leave the request hanging and still consume bandwidth in the background and lower the max allowed concurrent request being made while it's still in process.

Instead use the AbortController to actually abort the request, Here is an example

const controller = new AbortController()

// 5 second timeout:
const timeoutId = setTimeout(() => controller.abort(), 5000)

fetch(url, { signal: controller.signal }).then(response => {
  // completed request before timeout fired

  // If you only wanted to timeout the request, not the response, add:
  // clearTimeout(timeoutId)
})

^{AbortController can be used for other things as well, not only fetch but for readable/writable streams as well. More newer functions (specially promise based ones) will use this more and more. NodeJS have also implemented AbortController into its streams/filesystem as well. I know web bluetooth are looking into it also. Now it can also be used with addEventListener option and have it stop listening when the signal ends}

  fetchTimeout (url,options,timeout=3000) {
    return new Promise( (resolve, reject) => {
      fetch(url, options)
      .then(resolve,reject)
      setTimeout(reject,timeout);
    })
  }

there's no timeout support in the fetch API yet. But it could be achieved by wrapping it in a promise.

for eg.

  function fetchWrapper(url, options, timeout) {
    return new Promise((resolve, reject) => {
      fetch(url, options).then(resolve, reject);

      if (timeout) {
        const e = new Error("Connection timed out");
        setTimeout(reject, timeout, e);
      }
    });
  }

Building on Endless' excellent answer, I created a helpful utility function.

const fetchTimeout = (url, ms, { signal, ...options } = {}) => {
    const controller = new AbortController();
    const promise = fetch(url, { signal: controller.signal, ...options });
    if (signal) signal.addEventListener("abort", () => controller.abort());
    const timeout = setTimeout(() => controller.abort(), ms);
    return promise.finally(() => clearTimeout(timeout));
};

1. If the timeout is reached before the resource is fetched then the fetch is aborted.
2. If the resource is fetched before the timeout is reached then the timeout is cleared.
3. If the input signal is aborted then the fetch is aborted and the timeout is cleared.

const controller = new AbortController();

document.querySelector("button.cancel").addEventListener("click", () => controller.abort());

fetchTimeout("example.json", 5000, { signal: controller.signal })
    .then(response => response.json())
    .then(console.log)
    .catch(error => {
        if (error.name === "AbortError") {
            // fetch aborted either due to timeout or due to user clicking the cancel button
        } else {
            // network error or json parsing error
        }
    });

Hope that helps.

If you haven't configured timeout in your code, It will be the default request timeout of your browser.

1) Firefox - 90 seconds

Type about:config in Firefox URL field. Find the value corresponding to key network.http.connection-timeout

2) Chrome - 300 seconds

Source

I really like the clean approach from this gist using Promise.race

fetchWithTimeout.js

export default function (url, options, timeout = 7000) {
    return Promise.race([
        fetch(url, options),
        new Promise((_, reject) =>
            setTimeout(() => reject(new Error('timeout')), timeout)
        )
    ]);
}

main.js

import fetch from './fetchWithTimeout'

// call as usual or with timeout as 3rd argument

fetch('http://google.com', options, 5000) // throw after max 5 seconds timeout error
.then((result) => {
    // handle result
})
.catch((e) => {
    // handle errors and timeout error
})