Hook equivalent for `getSnapshotBeforeUpdate`

[brainkim]

Do you want to request a feature or report a bug?

Feature

What is the current behavior?

There is no hook based equivalent for getSnapshotBeforeUpdate. The docs state:

Our goal is for Hooks to cover all use cases for classes as soon as possible. There are no Hook equivalents to the uncommon getSnapshotBeforeUpdate and componentDidCatch lifecycles yet, but we plan to add them soon.

What is the expected behavior?

There is a hook based equivalent for getSnapshotBeforeUpdate, maybe something like:

function ScrollingList(props) {
  const lengthRef = React.useRef(0);
  const listRef = React.useRef(null);

  const prevHeight = React.useSnapshot(() => {
    if (lengthRef.current < props.list.length) {
      const list = listRef.current;
      return list.scrollHeight - list.scrollTop;
    }
  }); 

  React.useEffect(() => {
    lengthRef.current = props.list.length;
  }, [props.list.length]);

  React.useEffect(() => {
    if (prevHeight != null) {
      const list = listRef.current;
      list.scrollTop = list.scrollHeight - prevHeight;
    }
  }, [prevHeight]);
  return (
    <div ref={listRef}>{/* ... */}</div>
  );
}

This code probably is bug-ridden and not the best use of hooks but you get the idea.

I’d like to know:

1. If this feature is planned or on the roadmap.
2. What the proposed API will be.
3. If anyone is working on this.

Sorry, if this is being tracked somewhere and I haven’t seen it. I’m planning an intense component which will use getSnapshotBeforeUpdate and I’d love some guidance about the future of this lifecycle method.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

React v16.8.0 and later. All browsers and OSes.

[brainkim]

@gaearon Maybe this could be moved to reactjs/rfcs for more visibility?

[voliva]

It's been almost a year since this hook is marked as "Coming soon™" in the hooks FAQ, but I don't see much movement here... And this would be useful to build hooks that need to run something before the component updates (such as the example which deals with scroll positions before/after update).

Is there any chance this will be looked in the near future™? I completely agree figuring out the API for this hook is a quite hard, so I'm quite sure there will be a big discussion around it.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contribution.

[brainkim]

😭 stale bot why are you like this.

[META-DREAMER]

I hacked around this by using useMemo since that runs the code before the render. For example, to trigger LayoutAnimation in react native:

export const useLayoutAnimation = (
  deps: unknown[],
  easing: LayoutAnimationEasingFunction = 'easeInEaseOut',
) => {
  useMemo(() => {
    LayoutAnimation[easing]();
  }, [...deps, easing]);
};

[ivan7237d]

The workaround that I use is to have a component like this:

import * as React from 'react';

export class GetSnapshotBeforeUpdate extends React.Component<{
  callback?: VoidFunction;
}> {
  getSnapshotBeforeUpdate = () => {
    this.props.callback?.();
    // Prevents warning.
    return null;
  };

  // Prevents warning.
  componentDidUpdate = () => {};

  render = () => null;
}

and then stick <GetSnapshotBeforeUpdate callback={() => {...} /> into the rendered output of a functional component. If anyone notices any issues with this approach, pls let me know!

BTW I was very surprised that the cleanup function of useLayoutEffect isn't run at the same point as getSnapshotBeforeUpdate.

[stale]

This issue has been automatically marked as stale. If this issue is still affecting you, please leave any comment (for example, "bump"), and we'll keep it open. We are sorry that we haven't been able to prioritize it yet. If you have any new additional information, please include it with your comment!

[stale]

Closing this issue after a prolonged period of inactivity. If this issue is still present in the latest release, please create a new issue with up-to-date information. Thank you!

[aweary]

Re-opening as it's still an active feature request