expo/use-unmount-signal

A React Hook to cancel promises when a component is unmounted

use-unmount-signal

useUnmountSignal is a React Hook to cancel promises when a component is unmounted. It uses the W3C-standard AbortSignal API to notify compatible promises when the calling component is unmounted.

API

useUnmountSignal(): AbortSignal

A React Hook that returns an AbortSignal object that is marked as aborted when the calling component is unmounted.

Example

import useUnmountSignal from 'use-unmount-signal';

function Example() {
  // useUnmountSignal returns an AbortSignal object that APIs like fetch accept
  const unmountSignal = useUnmountSignal();
  return (
    <button
      onClick={() =>
        fetch('https://ping.example.com', { signal: unmountSignal })
      }>
      Ping
    </button>
  );
}

With async function event handlers

The HTML5 specification says:

Any web platform API using promises to represent operations that can be aborted must adhere to the following:

• Accept AbortSignal objects through a signal dictionary member.
• Convey that the operation got aborted by rejecting the promise with an "AbortError" DOMException.
• Reject immediately if the AbortSignal's aborted flag is already set, otherwise:
• Use the abort algorithms mechanism to observe changes to the AbortSignal object and do so in a manner that does not lead to clashes with other observers.

Calling any async function creates a promise. Therefore, authors of async functions need to follow the above guidance to write abortable functions.

import { useState } from 'react';
import useUnmountSignal from 'use-unmount-signal';

function Example() {
  const unmountSignal = useUnmountSignal();
  const [status, setStatus] = useState('ready');

  const handleClick = useCallback(
    async () => {
      if (unmountSignal.aborted) { throw new AbortError(); }

      const response = await fetch('https://ping.example.com', { signal: unmountSignal });
      if (unmountSignal.aborted) { throw new AbortError(); }

      // We are guaranteed that the component is still mounted at this point
      if (response.ok) {
        setStatus('OK');
      } else {
        setStatus(response.status);
      }
    },
    [unmountSignal, setStatus]
  );

  return <button onClick={handleClick}>Ping {status}</button>;
}