Boxed Callback

This package provides a custom hook for creating immutable callback references, similar to pointers or bound class fields.

The problem

Currently useCallback will return a new function whenever a dependency updates thus triggering a rerender for all components that are receiving it as a prop, even if the component is wrapped with the memo HOC. Example:

function ClickCounter({onClick}) {
  const [clicks, setClicks] = useState(0);
  const onClick = useCallback(() => {
    setClicks(clicks + 1);
  }, [clicks]);

  return (
    <>
      <p>Clicked {clicks} times</p>
      <MyButton onClick={onClick} />
    </>
  );
}

Here, <MyButton> will always rerender when the amount of clicks changes because we need clicks as a dependency inside the onClick callback for it to work properly. We could easily solve this by passing a reducer to setClicks instead of incrementing a variable from outside our callback:

const onClick = useCallback(() => setClicks(amount => amount + 1, []));

The problem is that it's not always that easy, specially when intercepting and forwarding props from the parent/context to the children.

The solution

This package acts in a similar way to useCallback but it stores your callback inside a mutable reference and returns an immutable function that calls the last function stored in that reference when triggered, thus providing the same functionality as useCallback with the benefit that the generated callback is always the same:

import useBoxedCallback from 'use-boxed-callback';

function ClickCounter({onClick}) {
  const [clicks, setClicks] = useState(0);

  // This works as expected and <MyButton> will only render a single time
  // during the whole life cycle of the component
  const onClick = useBoxedCallback(() => {
    setClicks(clicks + 1);
  });

  return (
    <>
      <p>Clicked {clicks} times</p>
      <MyButton onClick={onClick} />
    </>
  );
}

You can also pass additional arguments after the callback, they will be provided as additional arguments to the callback when triggered:

// The first arguments are the ones provided by the caller, the rest
// are the ones provided by useBoxedCallback
function incrementClicks(event, clicks, setClicks) {
  event.preventDefault();

  setClicks(clicks + 1);
}

function ClickCounter({onClick}) {
  const [clicks, setClicks] = useState(0);
  const onClick = useBoxedCallback(incrementClicks, clicks, setClicks);

  return (
    <>
      <p>Clicked {clicks} times</p>
      <button onClick={onClick}>Click me</button>
    </>
  );
}

ISC License

Copyright 2019 Alan Hoffmeister

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.