Thanks for the quick response.

Legacy timers do not support rAF:

I'm not sure why waitFor from @testing-library/dom was working before merged https://github.com/testing-library/dom-testing-library/pull/966 though. Maybe it just worked incidentally because we used to real setImmediate which would flush animation frames at some point (even though the timing would be completely off)

PR welcome!

Let me check if I can throw something together quickly. Not sure if this will be useful though since that would still require updating jest itself.

Legacy timers do not support rAF: https://github.com/facebook/jest/blob/d1882f2e6033186bd310240add41ffe50c2a9259/packages/jest-fake-timers/src/legacyFakeTimers.ts#L31-L40 (and jsdom uses its own setInterval, not the one exposed, so mocking one doesn't mock the other)

PR welcome!

We’re not yet asking application authors to try the release.

People won't listen (like me).

For example, TikTok has upgraded to React 18 already (https://twitter.com/Brooooook_lyn/status/1402632529270632456?s=20)

Since people want to try out fresh things immediately, I think a list of what is blocking people from upgrading is helpful and can reduce other one's time-wasting.

<!-- Please provide a clear and concise description of what the bug is. Include screenshots if needed. Please test using the latest version of the relevant React packages to make sure your issue has not already been fixed. -->

React version: 17.0.2

Steps To Reproduce

1. Render a button and a scrollable list with a height of 150px. The list should contain an array of 15 items, making sure to set the key prop of each item to unique values.
2. Observe that you can see around 8 of the original 15 list items in view.
3. On clicking the button, insert 15 more items into the beginning of the list, once again making sure to set the key prop of each item to unique values.
4. Observe that you can now see around 8 of the new list items in view.

<!-- Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Issues without reproduction steps or code examples may be immediately closed as not actionable. -->

Link to code example: https://codesandbox.io/s/keen-sound-7q5yf?file=/src/App.js

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The current behavior

If the scroll position is at the very top of a list, after inserting new items at the beginning of the list, the new items are now visible.

The expected behavior

If the scroll position is at the very top of a list, after inserting new items at the beginning of the list, the original items should remain visible.

NOTE: When the scroll position is 1 or more pixels from the top of a list, after inserting new items at the beginning of the list, the new items remain visible as expected.

Hi! Can you clarify what would be the purpose of an issue like this? We’re not yet asking application authors to try the release.

The Alpha is focused on the library maintainers, and there will be a several months period before the Beta. It’s expected things would need adjustment early on, and I’m worried making a list of popular libraries before the authors even got a chance to try the release might be a bit premature.

We are committed to working with library authors and helping find recommendations where they’re unclear, including on this issue tracker. I’m just not sure that making a public list is the right way to kick this off.

What do you think?

https://github.com/ReactTraining/react-router/issues/7870

I do not have permission to post https://github.com/reactwg/react-18/discussions. Please open and pin a new issue in that repo to list all widely-used library that does not work with React 18 or need special handling.

This issue seems to be solved by https://github.com/facebook/react/pull/18031

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs. Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs. Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs. Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.

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Summary

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Summary

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I've got the same problem - but this is potentially a duplicate of https://github.com/facebook/jest/issues/11500. This same issue is being/has been discussed in the comments on that issue

@mmnoo that's sort of what I was saying. Think of it is less as "rules", and think of it as "how is this going to potentially change behavior in my application?".

I can't give specifics, because I don't know your app and I don't know what side effects you're considering doing here.

If the "side effect" is logging to the console or writing to localStorage, then while it's technically "breaking the rules", it's meaningless in the grand scheme and won't cause bugs.

If it's, say, making an HTTP DELETE call at the wrong time... then that could be very bad for your app :)

So, try to think about behavior based on the stated way React is going to execute things, not "am I breaking the rules".

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<!-- 0 failure: 0 warning:

1 markdown notices DangerID: danger-id-stable; -->

Comparing: 1a106bdc2abc7af190b791d13b2ead0c2c556f7a...4b09c091809081be04a87986c45f8164a6ec7c0c

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

<p align="right"> Generated by :no_entry_sign: <a href="https://danger.systems/js">dangerJS</a> against 4b09c091809081be04a87986c45f8164a6ec7c0c </p>

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🐛 Bug Report

Callbacks scheduled with requestAnimationFrame are not called when using jest.useFakeTimers('legacy') and jest.advanceTimersByTime(17)

To Reproduce

test.each(["legacy", "modern"])(
  "%s fake timers wait for requestAnimationFrame",
  async (timerImplementation) => {
    jest.useFakeTimers(timerImplementation);
    let exited = false;
    // implemented in JSDOm with `setInterval(callback, 16.6666)`
    requestAnimationFrame(() => {
      exited = true;
    });

    jest.advanceTimersByTime(15);

    expect(exited).toBe(false);

    jest.advanceTimersByTime(2);

    expect(exited).toBe(true);
  }
);

Expected behavior

Tests pass with legacy and modern fake timers

Link to repl or repo (highly encouraged)

https://github.com/eps1lon/jest-fake-timers-request-animation-frame

envinfo

  System:
    OS: Linux 5.4 Ubuntu 20.04.2 LTS (Focal Fossa)
    CPU: (6) x64 Intel(R) Core(TM) i5-9400 CPU @ 2.90GHz
  Binaries:
    Node: 12.22.1 - ~/.nvm/versions/node/v12.22.1/bin/node
    Yarn: 1.22.5 - /usr/bin/yarn
    npm: 6.14.12 - ~/.nvm/versions/node/v12.22.1/bin/npm
  npmPackages:
    jest: ^27.0.4 => 27.0.4

Hi @houssemchebeb!

Thank you for your pull request and welcome to our community.

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Summary

Fix typo in react-devtools-shared

Hi. I just published a library and it contains a wrapper around Portals and it dodges this event bubbling behaviour by portal-ling the portal itself. I didn't really test the implementation but feel free to check it out.

Portal Renderer code - https://github.com/nibmz7/nimz-app/blob/main/core/utils/Portal/PortalRenderer.tsx Portal code - https://github.com/nibmz7/nimz-app/blob/main/core/utils/Portal/index.tsx The library if you intend to try it out - https://www.npmjs.com/package/nimz-utils

I haven't tried the library out myself actually 😅. If it doesn't work, you may copy for portals over to your project.

I just saw that there's actually an option called includePaths in the code related to this diffing. Maybe we could expose it in the CLI and people can choose freely, it'll be less risky than trying to guess this package.json/lockfile thing, will be non-breaking, and pretty flexible to whoever different needs anyone has.

https://github.com/facebook/jest/blob/bc50e7f360ab1845abbaa0b3ad788caead0d3174/packages/jest-changed-files/src/index.ts#L36

@SimenB what are your thoughts?

Just a suggestion

In React 18 , React should accept extra params to setState function so dev can specify what changed in more general terms that he/she can use in React.memo() to determine if that changes should re-render the specific component with the new data

it should be something like this

setState(
  [...state.users, user], 
  {action:'USER_ADDED', id : 'some_id'}
);

the broadcast can be any arbitrary data

and then in the User component, we can catch that broadcast in React.memo() like this

const User= (user)=>{
   // component code   
}

export default React.memo(User, (prev, next, brodcast)=>{
  if(broadcast?.action === 'ACTION_ADDED'  &&  next.id !== broadcast.id){
   // should not re-render this component
   return true;
 }
 return false;
});

this should work with batch setState as well just instead of object, broadcast should have an array of broadcasts

this will save the devs from deep comparison of props if it holds a lot of data nodes in it.

@markerikson that is a very useful explanation, thanks for taking the time to write it.

I think I have another solution to my specific problem that is less convoluted than a useEffect. (Munging ui (focus) state with data state as a tradeoff).

If I were to pollute my reducer with a side effect and there was no downside to redundant calls to that side effect, is there still a risk of issues with your understanding?

Just curious where rules can be bent. Not meaning to call all of FP ideology as I quite like it. Although when blindly followed anything start to feel that way :)

Also in very much need of this in a monorepo setup.

I'd say implementing this over the package.json would be simpler, as if it's done checking the lockfile there will be so many different formats to take into account: NPM shrinkwrap, NPM package-lock, Yarn Classic, Yarn Berry (not sure, but I guess it changed), pnpm (please!).

The downside of not checking the lockfiles is that if just the lockfile is updated (e.g security upgrades from Dependabot) then again it could lead to things breaking unexpectedly.

What’s the idiomatic way to do cleanup for things that aren’t async, but just require disposal?

Here is one example above (I like it and go back to it because I know it well - but it's similar for other sync APIs going forward):

const ac = new AbortController();
const { signal } = ac;
const element = getElementSomeHow();
element.addEventListener('click', onClick, { signal });
element.addEventListener('mousedown', onMouseDown, { signal });
element.addEventListener('mouseup', onMouseUp, { signal });
// eventually we want to cleanup
ac.abort(); // removes all listeners

@gaearon that's a good point, if you look carefully you'll see a bunch of the other APIs we have are more IDisposable than CancellationToken. The addEventListener example above is a good example.

Given the web converged on "disinterest semantics" for cancellation (cancellation is a request rather than an error) - the line between "cancellation" and "disposing a resource" is hair-thin (dispose a resource but cancel an action mostly).

However - for React in particular I think these sort of semantics make a ton of sense:

• Something like IDisposable typically means "you have to dispose it now when the user does .dispose. It typically comes with life-time management guarantees (like try using in the JS proposal case) which is the opposite of what frameworks would want (to control the lifecycle).
• Cancellation semantics like with AbortSignal mean "the producer upstream has expressed disinterest in this action" (data fetching, uploads, sockets listening, file actions, workers etc) - this gives React and the calling code a lot more flexibility.

_{Note: A logical next step is to loop in some more WHATWG involved folks.}

_{Note 2: I'm happy to loop in some of the .NET folks as well as some of the .NET folks who moved from C# to TS if that'd help but I'd like to keep the scope of the ask/discussion here small - aligning React with web platform APIs with regards to AbortSignal. Stuff like explicit resource management would be great to have but would not map well to React's use case where the framework needs to control the lifetime of resources rather than the calling code.}

I think conceptually it doesn’t feel like the right fit to me because (in .NET terms) effect cleanup is more like IDisposable than CancellationToken. But that’s just my hunch so I would need to see more comparisons to understand if there’s a real problem or I’m making it up.

What’s the idiomatic way to do cleanup for things that aren’t async, but just require disposal?

Yes, it's the undefined that's the problem for the cleanup case :)

I suspect it'll be even more so when concurrent mode becomes "the norm".

Though really - between "force everyone to return a function" and "take an AbortSignal argument like web APIs" I'd pick the latter as it makes for a much nicer API that "throws you to the pit of success" more often.

if react threw an error (at least in developer builds) if a function isn't returned from useEffect that would also be a nice change.

Hmm. I thought we are throwing an error if what you return is neither undefined nor a function.