[Fiber] Don't Rethrow Errors at the Root #28627
Merged
+1,495
−1,037
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
facebook-github-bot
added
CLA Signed
React Core Team
sebmarkbage
commented
Mar 25, 2024
| logCapturedError( | ||
| root.current, | ||
| createCapturedValueAtFiber(error, root.current), | ||
| ); |
There was a problem hiding this comment.
Instead of stashing this and then logging, I just log it directly. I think that's fine since nothing else is really supposed to be happening in between but not sure. We can do that now since it's not rethrowing so we still will finish the commit after the log.
|
Comparing: 5910eb3...0928d91 Critical size changesIncludes critical production bundles, as well as any change greater than 2%:
Significant size changesIncludes any change greater than 0.2%: Expand to show |
sebmarkbage
force-pushed
the
errorcallbacks
branch
from
d6a24f1 to
084ab0d
Compare
sebmarkbage
commented
Mar 25, 2024
| event.preventDefault(); | ||
| caughtErrors.push(event.error); | ||
| } | ||
| window.addEventListener('error', errorHandler); |
There was a problem hiding this comment.
We don't have "act" in the TypeScript environment.
| @@ -140,6 +142,6 @@ describe('ReactFlushSync (AggregateError not available)', () => { | |||
| // AggregateError is not available, React throws the first error, then | |||
| // throws the remaining errors in separate tasks. | |||
| expect(error).toBe(aahh); | |||
| expect(flushFakeMicrotasks).toThrow(nooo); | |||
| await flushFakeMicrotasks(); | |||
There was a problem hiding this comment.
Should we assert somewhere that this was thrown to reportError or whatever?
There was a problem hiding this comment.
So it's a bit weird about what we should be testing here. Because this is to test that something works even if aggregated errors is not supported by the platform. However, we only do aggregation at all in act() now. So we're testing act() and if you use act in an environment that doesn't support aggregated errors, then this does get dropped. Not logged somewhere else.
Which I guess is mostly if you use act in a non-JSDOM environment.
There was a problem hiding this comment.
Makes sense, we should probably update the comment on 143 then
packages/react-reconciler/src/__tests__/ReactIncrementalErrorLogging-test.js
Show resolved
Hide resolved
| expect.objectContaining({ | ||
| message: 'Boom', | ||
| }), | ||
| ], | ||
| ]); | ||
| expect(console.warn.mock.calls).toEqual([ |
There was a problem hiding this comment.
We're moving some logs from console.error to console.warn right? Can we add that to the "Breaking changes" in the description?
There was a problem hiding this comment.
So it used to be that we had two logs. One for the error and then one for the suffix. In my previous PR removing invokeGuardedCallback I was able to unify them into one but what this is doing is basically restoring it into two because we can't pass a component stack to reportGlobalError for uncaught but we can for caught which just goes to console.error.
It really isn't great to have the two logs, especially if the former gets called with preventDefault which used to silence the second one but we can't do that anymore.
I'm kind of inclined to say that we shouldn't have this second log at all and let uncaught not have component stacks by default and instead if you want that you implement it yourself using onUncaughtError.
There was a problem hiding this comment.
I like it. But why switch from error to warn?
Would using onUncaughtError result in double logging or would we not use reportGlobalError if that's provided?
There was a problem hiding this comment.
The warn is mainly about telling you to add an error boundary. It's not really so much about the component stack anymore although it includes it. Where as before it was more like two console.error as a pair. The console.warn can stand on its own.
You should really always have a root error boundary and if you don't want to you should at least implement onUncaughtError. So this shouldn't really be a case you need to hit beyond seeing the warning.
onUncaughtError takes control so this doesn't get logged then.
|
[WIP comment] I'm going to update this as I go through it Making some notes as I fix the tests, it looks like these are some changes included: Internal Tests
Single error // TODO: why do some of my assertions require the extra array and not others?
await expect(async () => {
await act(() => {
root.render(<WithError />);
});
}).rejects.toThrow(
expect.objectContaining({
message: "Boom",
}),
);Multiple errors with asymmetric matchers await expect(async () => {
await act(() => {
root.render(<WithError />);
});
}).rejects.toThrow(
expect.objectContaining({
errors: [
expect.objectContaining({
message: "Boom",
}),
expect.objectContaining({
message: "Boom",
}),
],
}),
);Multiple errors with error constructors await expect(async () => {
await act(() => {
root.render(<WithError />);
});
}).rejects.toThrow(
// eslint-disable-next-line no-undef
new AggregateError([
new Error('Boom'),
new Error('Boom'),
]),
);Multiple errors with waitForThrow helper root.render(<WithError /).
const aggregateError = await waitForThrow();
expect(aggregateError.errors.length).toBe(2);
expect(aggregateError.errors[0].message).toContain('Boom');
expect(aggregateError.errors[0].message).toContain('Boom');Public builds
|
|
Things that suck about the
|
|
I fixed the legacy tests but there's still two non-legacy left: Remaining tests to fix
|
| 'Warning: React.jsx: type is invalid -- expected a string ' + | ||
| '(for built-in components) or a class/function ' + | ||
| '(for composite components) but got: null.', | ||
| {withoutStack: 1}, |
There was a problem hiding this comment.
I don't understand why this switched from React.createElement to React.jsx?
I assume that's also why there's no component stack either?
There was a problem hiding this comment.
It wasn't actually asserted before because the render threw which means the assertion wasn't run. The assertion before was asserting the wrong thing.
| }).toErrorDev( | ||
| 'Expected the last optional `callback` argument to be ' + | ||
| 'a function. Instead received: no.', | ||
| {withoutStack: 1}, |
There was a problem hiding this comment.
Many of the test changes here removed the component stacks, is that expected?
There was a problem hiding this comment.
These are the same. They weren't actually asserting before.
These should always be inside of DOM event listeners anyway. This lets us report more than one error. Not sure what to do about the React Native one.
This ensures that they can get logged properly through the regular onerror mechanism.
Also let waitForThrow listen to global errors too.
We try to throw the first error discovered even if other errors happen later which more closely models what used to happen when the act scope was aborted early.
This way you can nest internalAct/waitFor.
Since act now swallows the logging, we need to use a fakeAct to test these cases. Since there's no rethrow, only logging, this case doesn't throw the original error anymore.
…rors Such as errors logged in event handlers and onRecoverableErrors. This is different from the public act which doesn't catch those.
sebmarkbage
force-pushed
the
errorcallbacks
branch
from
f9ac852 to
613ae34
Compare
github-actions bot
pushed a commit
that referenced
this pull request
Mar 27, 2024
Stacked on top of #28498 for test fixes. ### Don't Rethrow When we started React it was 1:1 setState calls a series of renders and if they error, it errors where the setState was called. Simple. However, then batching came and the error actually got thrown somewhere else. With concurrent mode, it's not even possible to get setState itself to throw anymore. In fact, all APIs that can rethrow out of React are executed either at the root of the scheduler or inside a DOM event handler. If you throw inside a React.startTransition callback that's sync, then that will bubble out of the startTransition but if you throw inside an async callback or a useTransition we now need to handle it at the hook site. So in 19 we need to make all React.startTransition swallow the error (and report them to reportError). The only one remaining that can throw is flushSync but it doesn't really make sense for it to throw at the callsite neither because batching. Just because something rendered in this flush doesn't mean it was rendered due to what was just scheduled and doesn't mean that it should abort any of the remaining code afterwards. setState is fire and forget. It's send an instruction elsewhere, it's not part of the current imperative code. Error boundaries never rethrow. Since you should really always have error boundaries, most of the time, it wouldn't rethrow anyway. Rethrowing also actually currently drops errors on the floor since we can only rethrow the first error, so to avoid that we'd need to call reportError anyway. This happens in RN events. The other issue with rethrowing is that it logs an extra console.error. Since we're not sure that user code will actually log it anywhere we still log it too just like we do with errors inside error boundaries which leads all of these to log twice. The goal of this PR is to never rethrow out of React instead, errors outside of error boundaries get logged to reportError. Event system errors too. ### Breaking Changes The main thing this affects is testing where you want to inspect the errors thrown. To make it easier to port, if you're inside `act` we track the error into act in an aggregate error and then rethrow it at the root of `act`. Unlike before though, if you flush synchronously inside of act it'll still continue until the end of act before rethrowing. I expect most user code breakages would be to migrate from `flushSync` to `act` if you assert on throwing. However, in the React repo we also have `internalAct` and the `waitForThrow` helpers. Since these have to use public production implementations we track these using the global onerror or process uncaughtException. Unlike regular act, includes both event handler errors and onRecoverableError by default too. Not just render/commit errors. So I had to account for that in our tests. We restore logging an extra log for uncaught errors after the main log with the component stack in it. We use `console.warn`. This is not yet ignorable if you preventDefault to the main error event. To avoid confusion if you don't end up logging the error to console I just added `An error occurred`. ### Polyfill All browsers we support really supports `reportError` but not all test and server environments do, so I implemented a polyfill for browser and node in `shared/reportGlobalError`. I don't love that this is included in all builds and gets duplicated into isomorphic even though it's not actually needed in production. Maybe in the future we can require a polyfill for this. ### Follow Ups In a follow up, I'll make caught vs uncaught error handling be configurable too. --------- Co-authored-by: Ricky Hanlon <rickhanlonii@gmail.com> DiffTrain build for [6786563](6786563)
sebmarkbage
added a commit
that referenced
this pull request
Mar 27, 2024
Stacked on #28627. This makes error logging configurable using these `createRoot`/`hydrateRoot` options: ``` onUncaughtError(error: mixed, errorInfo: {componentStack?: ?string}) => void onCaughtError(error: mixed, errorInfo: {componentStack?: ?string, errorBoundary?: ?React.Component<any, any>}) => void onRecoverableError(error: mixed, errorInfo: {digest?: ?string, componentStack?: ?string}) => void ``` We already have the `onRecoverableError` option since before. Overriding these can be used to implement custom error dialogs (with access to the `componentStack`). It can also be used to silence caught errors when testing an error boundary or if you prefer not getting logs for caught errors that you've already handled in an error boundary. I currently expose the error boundary instance but I think we should probably remove that since it doesn't make sense for non-class error boundaries and isn't very useful anyway. It's also unclear what it should do when an error is rethrown from one boundary to another. Since these are public APIs now we can implement the ReactFiberErrorDialog forks using these options at the roots of the builds. So I unforked those files and instead passed a custom option for the native and www builds. To do this I had to fork the ReactDOMLegacy file into ReactDOMRootFB which is a duplication but that will go away as soon as the FB fork is the only legacy root.
github-actions bot
pushed a commit
that referenced
this pull request
Mar 27, 2024
Stacked on #28627. This makes error logging configurable using these `createRoot`/`hydrateRoot` options: ``` onUncaughtError(error: mixed, errorInfo: {componentStack?: ?string}) => void onCaughtError(error: mixed, errorInfo: {componentStack?: ?string, errorBoundary?: ?React.Component<any, any>}) => void onRecoverableError(error: mixed, errorInfo: {digest?: ?string, componentStack?: ?string}) => void ``` We already have the `onRecoverableError` option since before. Overriding these can be used to implement custom error dialogs (with access to the `componentStack`). It can also be used to silence caught errors when testing an error boundary or if you prefer not getting logs for caught errors that you've already handled in an error boundary. I currently expose the error boundary instance but I think we should probably remove that since it doesn't make sense for non-class error boundaries and isn't very useful anyway. It's also unclear what it should do when an error is rethrown from one boundary to another. Since these are public APIs now we can implement the ReactFiberErrorDialog forks using these options at the roots of the builds. So I unforked those files and instead passed a custom option for the native and www builds. To do this I had to fork the ReactDOMLegacy file into ReactDOMRootFB which is a duplication but that will go away as soon as the FB fork is the only legacy root. DiffTrain build for [a053716](a053716)
5 tasks
EdisonVan
pushed a commit
to EdisonVan/react
that referenced
this pull request
Apr 15, 2024
Stacked on top of facebook#28498 for test fixes. ### Don't Rethrow When we started React it was 1:1 setState calls a series of renders and if they error, it errors where the setState was called. Simple. However, then batching came and the error actually got thrown somewhere else. With concurrent mode, it's not even possible to get setState itself to throw anymore. In fact, all APIs that can rethrow out of React are executed either at the root of the scheduler or inside a DOM event handler. If you throw inside a React.startTransition callback that's sync, then that will bubble out of the startTransition but if you throw inside an async callback or a useTransition we now need to handle it at the hook site. So in 19 we need to make all React.startTransition swallow the error (and report them to reportError). The only one remaining that can throw is flushSync but it doesn't really make sense for it to throw at the callsite neither because batching. Just because something rendered in this flush doesn't mean it was rendered due to what was just scheduled and doesn't mean that it should abort any of the remaining code afterwards. setState is fire and forget. It's send an instruction elsewhere, it's not part of the current imperative code. Error boundaries never rethrow. Since you should really always have error boundaries, most of the time, it wouldn't rethrow anyway. Rethrowing also actually currently drops errors on the floor since we can only rethrow the first error, so to avoid that we'd need to call reportError anyway. This happens in RN events. The other issue with rethrowing is that it logs an extra console.error. Since we're not sure that user code will actually log it anywhere we still log it too just like we do with errors inside error boundaries which leads all of these to log twice. The goal of this PR is to never rethrow out of React instead, errors outside of error boundaries get logged to reportError. Event system errors too. ### Breaking Changes The main thing this affects is testing where you want to inspect the errors thrown. To make it easier to port, if you're inside `act` we track the error into act in an aggregate error and then rethrow it at the root of `act`. Unlike before though, if you flush synchronously inside of act it'll still continue until the end of act before rethrowing. I expect most user code breakages would be to migrate from `flushSync` to `act` if you assert on throwing. However, in the React repo we also have `internalAct` and the `waitForThrow` helpers. Since these have to use public production implementations we track these using the global onerror or process uncaughtException. Unlike regular act, includes both event handler errors and onRecoverableError by default too. Not just render/commit errors. So I had to account for that in our tests. We restore logging an extra log for uncaught errors after the main log with the component stack in it. We use `console.warn`. This is not yet ignorable if you preventDefault to the main error event. To avoid confusion if you don't end up logging the error to console I just added `An error occurred`. ### Polyfill All browsers we support really supports `reportError` but not all test and server environments do, so I implemented a polyfill for browser and node in `shared/reportGlobalError`. I don't love that this is included in all builds and gets duplicated into isomorphic even though it's not actually needed in production. Maybe in the future we can require a polyfill for this. ### Follow Ups In a follow up, I'll make caught vs uncaught error handling be configurable too. --------- Co-authored-by: Ricky Hanlon <rickhanlonii@gmail.com>
EdisonVan
pushed a commit
to EdisonVan/react
that referenced
this pull request
Apr 15, 2024
Stacked on facebook#28627. This makes error logging configurable using these `createRoot`/`hydrateRoot` options: ``` onUncaughtError(error: mixed, errorInfo: {componentStack?: ?string}) => void onCaughtError(error: mixed, errorInfo: {componentStack?: ?string, errorBoundary?: ?React.Component<any, any>}) => void onRecoverableError(error: mixed, errorInfo: {digest?: ?string, componentStack?: ?string}) => void ``` We already have the `onRecoverableError` option since before. Overriding these can be used to implement custom error dialogs (with access to the `componentStack`). It can also be used to silence caught errors when testing an error boundary or if you prefer not getting logs for caught errors that you've already handled in an error boundary. I currently expose the error boundary instance but I think we should probably remove that since it doesn't make sense for non-class error boundaries and isn't very useful anyway. It's also unclear what it should do when an error is rethrown from one boundary to another. Since these are public APIs now we can implement the ReactFiberErrorDialog forks using these options at the roots of the builds. So I unforked those files and instead passed a custom option for the native and www builds. To do this I had to fork the ReactDOMLegacy file into ReactDOMRootFB which is a duplication but that will go away as soon as the FB fork is the only legacy root.
bigfootjon
pushed a commit
that referenced
this pull request
Apr 18, 2024
Stacked on top of #28498 for test fixes. ### Don't Rethrow When we started React it was 1:1 setState calls a series of renders and if they error, it errors where the setState was called. Simple. However, then batching came and the error actually got thrown somewhere else. With concurrent mode, it's not even possible to get setState itself to throw anymore. In fact, all APIs that can rethrow out of React are executed either at the root of the scheduler or inside a DOM event handler. If you throw inside a React.startTransition callback that's sync, then that will bubble out of the startTransition but if you throw inside an async callback or a useTransition we now need to handle it at the hook site. So in 19 we need to make all React.startTransition swallow the error (and report them to reportError). The only one remaining that can throw is flushSync but it doesn't really make sense for it to throw at the callsite neither because batching. Just because something rendered in this flush doesn't mean it was rendered due to what was just scheduled and doesn't mean that it should abort any of the remaining code afterwards. setState is fire and forget. It's send an instruction elsewhere, it's not part of the current imperative code. Error boundaries never rethrow. Since you should really always have error boundaries, most of the time, it wouldn't rethrow anyway. Rethrowing also actually currently drops errors on the floor since we can only rethrow the first error, so to avoid that we'd need to call reportError anyway. This happens in RN events. The other issue with rethrowing is that it logs an extra console.error. Since we're not sure that user code will actually log it anywhere we still log it too just like we do with errors inside error boundaries which leads all of these to log twice. The goal of this PR is to never rethrow out of React instead, errors outside of error boundaries get logged to reportError. Event system errors too. ### Breaking Changes The main thing this affects is testing where you want to inspect the errors thrown. To make it easier to port, if you're inside `act` we track the error into act in an aggregate error and then rethrow it at the root of `act`. Unlike before though, if you flush synchronously inside of act it'll still continue until the end of act before rethrowing. I expect most user code breakages would be to migrate from `flushSync` to `act` if you assert on throwing. However, in the React repo we also have `internalAct` and the `waitForThrow` helpers. Since these have to use public production implementations we track these using the global onerror or process uncaughtException. Unlike regular act, includes both event handler errors and onRecoverableError by default too. Not just render/commit errors. So I had to account for that in our tests. We restore logging an extra log for uncaught errors after the main log with the component stack in it. We use `console.warn`. This is not yet ignorable if you preventDefault to the main error event. To avoid confusion if you don't end up logging the error to console I just added `An error occurred`. ### Polyfill All browsers we support really supports `reportError` but not all test and server environments do, so I implemented a polyfill for browser and node in `shared/reportGlobalError`. I don't love that this is included in all builds and gets duplicated into isomorphic even though it's not actually needed in production. Maybe in the future we can require a polyfill for this. ### Follow Ups In a follow up, I'll make caught vs uncaught error handling be configurable too. --------- Co-authored-by: Ricky Hanlon <rickhanlonii@gmail.com> DiffTrain build for commit 6786563.
bigfootjon
pushed a commit
that referenced
this pull request
Apr 18, 2024
Stacked on #28627. This makes error logging configurable using these `createRoot`/`hydrateRoot` options: ``` onUncaughtError(error: mixed, errorInfo: {componentStack?: ?string}) => void onCaughtError(error: mixed, errorInfo: {componentStack?: ?string, errorBoundary?: ?React.Component<any, any>}) => void onRecoverableError(error: mixed, errorInfo: {digest?: ?string, componentStack?: ?string}) => void ``` We already have the `onRecoverableError` option since before. Overriding these can be used to implement custom error dialogs (with access to the `componentStack`). It can also be used to silence caught errors when testing an error boundary or if you prefer not getting logs for caught errors that you've already handled in an error boundary. I currently expose the error boundary instance but I think we should probably remove that since it doesn't make sense for non-class error boundaries and isn't very useful anyway. It's also unclear what it should do when an error is rethrown from one boundary to another. Since these are public APIs now we can implement the ReactFiberErrorDialog forks using these options at the roots of the builds. So I unforked those files and instead passed a custom option for the native and www builds. To do this I had to fork the ReactDOMLegacy file into ReactDOMRootFB which is a duplication but that will go away as soon as the FB fork is the only legacy root. DiffTrain build for commit a053716.
This was referenced Apr 24, 2024
henriettelienrebnor
pushed a commit
to equinor/Dexpi2Imf
that referenced
this pull request
Apr 23, 2025
<h3>Snyk has created this PR to upgrade react from 19.0.0 to
19.1.0.</h3>
:information_source: Keep your dependencies up-to-date. This makes it
easier to fix existing vulnerabilities and to more quickly identify and
fix newly disclosed vulnerabilities when they affect your project.
<hr/>
- The recommended version is **78 versions** ahead of your current
version.
- The recommended version was released **22 days ago**.
<details>
<summary><b>Release notes</b></summary>
<br/>
<details>
<summary>Package name: <b>react</b></summary>
<ul>
<li>
<b>19.1.0</b> - <a
href="https://redirect.github.com/facebook/react/releases/tag/v19.1.0">2025-03-28</a></br><h3>Owner
Stack</h3>
<p>An Owner Stack is a string representing the components that are
directly responsible for rendering a particular component. You can log
Owner Stacks when debugging or use Owner Stacks to enhance error
overlays or other development tools. Owner Stacks are only available in
development builds. Component Stacks in production are unchanged.</p>
<ul>
<li>An Owner Stack is a development-only stack trace that helps identify
which components are responsible for rendering a particular component.
An Owner Stack is distinct from a Component Stacks, which shows the
hierarchy of components leading to an error.</li>
<li>The <a href="https://react.dev/reference/react/captureOwnerStack"
rel="nofollow">captureOwnerStack API</a> is only available in
development mode and returns a Owner Stack, if available. The API can be
used to enhance error overlays or log component relationships when
debugging. <a
href="https://redirect.github.com/facebook/react/pull/29923"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29923/hovercard">#29923</a>, <a
href="https://redirect.github.com/facebook/react/pull/32353"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32353/hovercard">#32353</a>, <a
href="https://redirect.github.com/facebook/react/pull/30306"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30306/hovercard">#30306</a>,<br>
<a href="https://redirect.github.com/facebook/react/pull/32538"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32538/hovercard">#32538</a>, <a
href="https://redirect.github.com/facebook/react/pull/32529"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32529/hovercard">#32529</a>, <a
href="https://redirect.github.com/facebook/react/pull/32538"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32538/hovercard">#32538</a></li>
</ul>
<h3>React</h3>
<ul>
<li>Enhanced support for Suspense boundaries to be used anywhere,
including the client, server, and during hydration. <a
href="https://redirect.github.com/facebook/react/pull/32069"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32069/hovercard">#32069</a>, <a
href="https://redirect.github.com/facebook/react/pull/32163"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32163/hovercard">#32163</a>, <a
href="https://redirect.github.com/facebook/react/pull/32224"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32224/hovercard">#32224</a>, <a
href="https://redirect.github.com/facebook/react/pull/32252"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32252/hovercard">#32252</a></li>
<li>Reduced unnecessary client rendering through improved hydration
scheduling <a
href="https://redirect.github.com/facebook/react/pull/31751"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31751/hovercard">#31751</a></li>
<li>Increased priority of client rendered Suspense boundaries <a
href="https://redirect.github.com/facebook/react/pull/31776"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31776/hovercard">#31776</a></li>
<li>Fixed frozen fallback states by rendering unfinished Suspense
boundaries on the client. <a
href="https://redirect.github.com/facebook/react/pull/31620"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31620/hovercard">#31620</a></li>
<li>Reduced garbage collection pressure by improving Suspense boundary
retries. <a href="https://redirect.github.com/facebook/react/pull/31667"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31667/hovercard">#31667</a></li>
<li>Fixed erroneous “Waiting for Paint” log when the passive effect
phase was not delayed <a
href="https://redirect.github.com/facebook/react/pull/31526"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31526/hovercard">#31526</a></li>
<li>Fixed a regression causing key warnings for flattened positional
children in development mode. <a
href="https://redirect.github.com/facebook/react/pull/32117"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32117/hovercard">#32117</a></li>
<li>Updated <code>useId</code> to use valid CSS selectors, changing
format from <code>:r123:</code> to <code>«r123»</code>. <a
href="https://redirect.github.com/facebook/react/pull/32001"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32001/hovercard">#32001</a></li>
<li>Added a dev-only warning for null/undefined created in useEffect,
useInsertionEffect, and useLayoutEffect. <a
href="https://redirect.github.com/facebook/react/pull/32355"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32355/hovercard">#32355</a></li>
<li>Fixed a bug where dev-only methods were exported in production
builds. React.act is no longer available in production builds. <a
href="https://redirect.github.com/facebook/react/pull/32200"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32200/hovercard">#32200</a></li>
<li>Improved consistency across prod and dev to improve compatibility
with Google Closure Complier and bindings <a
href="https://redirect.github.com/facebook/react/pull/31808"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31808/hovercard">#31808</a></li>
<li>Improve passive effect scheduling for consistent task yielding. <a
href="https://redirect.github.com/facebook/react/pull/31785"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31785/hovercard">#31785</a></li>
<li>Fixed asserts in React Native when
passChildrenWhenCloningPersistedNodes is enabled for OffscreenComponent
rendering. <a
href="https://redirect.github.com/facebook/react/pull/32528"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32528/hovercard">#32528</a></li>
<li>Fixed component name resolution for Portal <a
href="https://redirect.github.com/facebook/react/pull/32640"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32640/hovercard">#32640</a></li>
<li>Added support for beforetoggle and toggle events on the dialog
element. <a class="issue-link js-issue-link" data-error-text="Failed to
load title" data-id="2882132160" data-permission-text="Title is private"
data-url="https://github.com/facebook/react/issues/32479"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32479/hovercard"
href="https://redirect.github.com/facebook/react/pull/32479">#32479</a>
<a href="https://redirect.github.com/facebook/react/pull/32479"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32479/hovercard">#32479</a></li>
</ul>
<h3>React DOM</h3>
<ul>
<li>Fixed double warning when the <code>href</code> attribute is an
empty string <a
href="https://redirect.github.com/facebook/react/pull/31783"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31783/hovercard">#31783</a></li>
<li>Fixed an edge case where <code>getHoistableRoot()</code> didn’t work
properly when the container was a Document <a
href="https://redirect.github.com/facebook/react/pull/32321"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32321/hovercard">#32321</a></li>
<li>Removed support for using HTML comments (e.g. <code><!--
--></code>) as a DOM container. <a
href="https://redirect.github.com/facebook/react/pull/32250"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32250/hovercard">#32250</a></li>
<li>Added support for <code><script></code> and
<code><template></code> tags to be nested within
<code><select></code> tags. <a
href="https://redirect.github.com/facebook/react/pull/31837"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31837/hovercard">#31837</a></li>
<li>Fixed responsive images to be preloaded as HTML instead of headers
<a href="https://redirect.github.com/facebook/react/pull/32445"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32445/hovercard">#32445</a></li>
</ul>
<h3>use-sync-external-store</h3>
<ul>
<li>Added <code>exports</code> field to <code>package.json</code> for
<code>use-sync-external-store</code> to support various entrypoints. <a
href="https://redirect.github.com/facebook/react/pull/25231"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25231/hovercard">#25231</a></li>
</ul>
<h3>React Server Components</h3>
<ul>
<li>Added <code>unstable_prerender</code>, a new experimental API for
prerendering React Server Components on the server <a
href="https://redirect.github.com/facebook/react/pull/31724"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31724/hovercard">#31724</a></li>
<li>Fixed an issue where streams would hang when receiving new chunks
after a global error <a
href="https://redirect.github.com/facebook/react/pull/31840"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31840/hovercard">#31840</a>, <a
href="https://redirect.github.com/facebook/react/pull/31851"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31851/hovercard">#31851</a></li>
<li>Fixed an issue where pending chunks were counted twice. <a
href="https://redirect.github.com/facebook/react/pull/31833"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31833/hovercard">#31833</a></li>
<li>Added support for streaming in edge environments <a
href="https://redirect.github.com/facebook/react/pull/31852"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31852/hovercard">#31852</a></li>
<li>Added support for sending custom error names from a server so that
they are available in the client for console replaying. <a
href="https://redirect.github.com/facebook/react/pull/32116"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32116/hovercard">#32116</a></li>
<li>Updated the server component wire format to remove IDs for hints and
console.log because they have no return value <a
href="https://redirect.github.com/facebook/react/pull/31671"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31671/hovercard">#31671</a></li>
<li>Exposed <code>registerServerReference</code> in client builds to
handle server references in different environments. <a
href="https://redirect.github.com/facebook/react/pull/32534"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32534/hovercard">#32534</a></li>
<li>Added react-server-dom-parcel package which integrates Server
Components with the <a href="https://parceljs.org/"
rel="nofollow">Parcel bundler</a> <a
href="https://redirect.github.com/facebook/react/pull/31725"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31725/hovercard">#31725</a>, <a
href="https://redirect.github.com/facebook/react/pull/32132"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32132/hovercard">#32132</a>, <a
href="https://redirect.github.com/facebook/react/pull/31799"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31799/hovercard">#31799</a>, <a
href="https://redirect.github.com/facebook/react/pull/32294"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/32294/hovercard">#32294</a>, <a
href="https://redirect.github.com/facebook/react/pull/31741"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31741/hovercard">#31741</a></li>
</ul>
</li>
<li>
<b>19.1.0-canary-ff628334-20250205</b> - 2025-02-06
</li>
<li>
<b>19.1.0-canary-fcb4e0f1-20250219</b> - 2025-02-20
</li>
<li>
<b>19.1.0-canary-fc8a898d-20241226</b> - 2024-12-27
</li>
<li>
<b>19.1.0-canary-fbcda19a-20250317</b> - 2025-03-17
</li>
<li>
<b>19.1.0-canary-f9d78089-20250306</b> - 2025-03-07
</li>
<li>
<b>19.1.0-canary-f83903bf-20250212</b> - 2025-02-12
</li>
<li>
<b>19.1.0-canary-f457d0b4-20250313</b> - 2025-03-13
</li>
<li>
<b>19.1.0-canary-f0edf41e-20250115</b> - 2025-01-14
</li>
<li>
<b>19.1.0-canary-ef979d47-20241218</b> - 2024-12-18
</li>
<li>
<b>19.1.0-canary-ef4bc8b4-20250328</b> - 2025-03-28
</li>
<li>
<b>19.1.0-canary-ebc22ef7-20250225</b> - 2025-02-26
</li>
<li>
<b>19.1.0-canary-e670e72f-20250214</b> - 2025-02-14
</li>
<li>
<b>19.1.0-canary-e1e74071-20250321</b> - 2025-03-21
</li>
<li>
<b>19.1.0-canary-e06c72fc-20241215</b> - 2024-12-16
</li>
<li>
<b>19.1.0-canary-e03ac20f-20250305</b> - 2025-03-05
</li>
<li>
<b>19.1.0-canary-de82912e-20241220</b> - 2024-12-20
</li>
<li>
<b>19.1.0-canary-de1eaa26-20250124</b> - 2025-01-24
</li>
<li>
<b>19.1.0-canary-db7dfe05-20250319</b> - 2025-03-19
</li>
<li>
<b>19.1.0-canary-d85cf3e5-20250205</b> - 2025-02-05
</li>
<li>
<b>19.1.0-canary-d55cc79b-20250228</b> - 2025-02-28
</li>
<li>
<b>19.1.0-canary-d46b04a2-20250117</b> - 2025-01-17
</li>
<li>
<b>19.1.0-canary-d4287258-20241217</b> - 2024-12-17
</li>
<li>
<b>19.1.0-canary-d331ba04-20250307</b> - 2025-03-10
</li>
<li>
<b>19.1.0-canary-cd90a4d8-20250210</b> - 2025-02-11
</li>
<li>
<b>19.1.0-canary-cbbe8666-20250213</b> - 2025-02-13
</li>
<li>
<b>19.1.0-canary-cabd8a0e-20250113</b> - 2025-01-13
</li>
<li>
<b>19.1.0-canary-c69a5fc5-20250318</b> - 2025-03-18
</li>
<li>
<b>19.1.0-canary-c492f975-20250128</b> - 2025-01-29
</li>
<li>
<b>19.1.0-canary-c01b8058-20241229</b> - 2024-12-30
</li>
<li>
<b>19.1.0-canary-bb9a24d9-20250130</b> - 2025-01-30
</li>
<li>
<b>19.1.0-canary-b3a95caf-20250113</b> - 2025-01-14
</li>
<li>
<b>19.1.0-canary-b158439a-20250115</b> - 2025-01-15
</li>
<li>
<b>19.1.0-canary-ae9017ce-20250122</b> - 2025-01-23
</li>
<li>
<b>19.1.0-canary-a84862db-20250218</b> - 2025-02-19
</li>
<li>
<b>19.1.0-canary-a4f9bd58-20250319</b> - 2025-03-20
</li>
<li>
<b>19.1.0-canary-a4b2d0d5-20250203</b> - 2025-02-03
</li>
<li>
<b>19.1.0-canary-9ff42a87-20250130</b> - 2025-01-31
</li>
<li>
<b>19.1.0-canary-9eabb373-20250124</b> - 2025-01-27
</li>
<li>
<b>19.1.0-canary-9b62ee71-20250122</b> - 2025-01-22
</li>
<li>
<b>19.1.0-canary-97d79495-20241223</b> - 2024-12-24
</li>
<li>
<b>19.1.0-canary-9463d51e-20241219</b> - 2024-12-19
</li>
<li>
<b>19.1.0-canary-93b58361-20250209</b> - 2025-02-10
</li>
<li>
<b>19.1.0-canary-8a7b487e-20250218</b> - 2025-02-18
</li>
<li>
<b>19.1.0-canary-8759c5c8-20250207</b> - 2025-02-07
</li>
<li>
<b>19.1.0-canary-7eb8234f-20241218</b> - 2024-12-18
</li>
<li>
<b>19.1.0-canary-7b402084-20250107</b> - 2025-01-07
</li>
<li>
<b>19.1.0-canary-74ea0c73-20250109</b> - 2025-01-09
</li>
<li>
<b>19.1.0-canary-740a4f7a-20250325</b> - 2025-03-25
</li>
<li>
<b>19.1.0-canary-7130d0c6-20241212</b> - 2024-12-12
</li>
<li>
<b>19.1.0-canary-6aa8254b-20250312</b> - 2025-03-12
</li>
<li>
<b>19.1.0-canary-694d3e1a-20241231</b> - 2025-01-01
</li>
<li>
<b>19.1.0-canary-6907aa2a-20241220</b> - 2024-12-23
</li>
<li>
<b>19.1.0-canary-662957cc-20250221</b> - 2025-02-21
</li>
<li>
<b>19.1.0-canary-62208bee-20250102</b> - 2025-01-02
</li>
<li>
<b>19.1.0-canary-5b51a2b9-20250116</b> - 2025-01-16
</li>
<li>
<b>19.1.0-canary-540efebc-20250112</b> - 2025-01-12
</li>
<li>
<b>19.1.0-canary-5398b711-20250314</b> - 2025-03-14
</li>
<li>
<b>19.1.0-canary-518d06d2-20241219</b> - 2024-12-19
</li>
<li>
<b>19.1.0-canary-4dff0e62-20241213</b> - 2024-12-13
</li>
<li>
<b>19.1.0-canary-4632e36a-20250216</b> - 2025-02-17
</li>
<li>
<b>19.1.0-canary-443b7ff2-20250303</b> - 2025-03-04
</li>
<li>
<b>19.1.0-canary-4280563b-20250326</b> - 2025-03-27
</li>
<li>
<b>19.1.0-canary-42687267-20250108</b> - 2025-01-08
</li>
<li>
<b>19.1.0-canary-3ce77d55-20250106</b> - 2025-01-06
</li>
<li>
<b>19.1.0-canary-3b009b4c-20250102</b> - 2025-01-03
</li>
<li>
<b>19.1.0-canary-37906d4d-20250127</b> - 2025-01-28
</li>
<li>
<b>19.1.0-canary-32b0cad8-20250213</b> - 2025-02-13
</li>
<li>
<b>19.1.0-canary-313332d1-20250326</b> - 2025-03-26
</li>
<li>
<b>19.1.0-canary-2980f277-20250301</b> - 2025-03-03
</li>
<li>
<b>19.1.0-canary-25677265-20250224</b> - 2025-02-24
</li>
<li>
<b>19.1.0-canary-22e39ea7-20250225</b> - 2025-02-25
</li>
<li>
<b>19.1.0-canary-18eaf51b-20250118</b> - 2025-01-20
</li>
<li>
<b>19.1.0-canary-130095f7-20241212</b> - 2024-12-12
</li>
<li>
<b>19.1.0-canary-0ca3deeb-20250311</b> - 2025-03-11
</li>
<li>
<b>19.1.0-canary-0a82580b-20250203</b> - 2025-02-04
</li>
<li>
<b>19.1.0-canary-056073de-20250109</b> - 2025-01-10
</li>
<li>
<b>19.1.0-canary-029e8bd6-20250306</b> - 2025-03-06
</li>
<li>
<b>19.0.0</b> - <a
href="https://redirect.github.com/facebook/react/releases/tag/v19.0.0">2024-12-05</a></br><p>Below
is a list of all new features, APIs, deprecations, and breaking changes.
Read <a href="https://react.dev/blog/2024/04/25/react-19"
rel="nofollow">React 19 release post</a> and <a
href="https://react.dev/blog/2024/04/25/react-19-upgrade-guide"
rel="nofollow">React 19 upgrade guide</a> for more information.</p>
<blockquote>
<p>Note: To help make the upgrade to React 19 easier, we’ve published a
react@18.3 release that is identical to 18.2 but adds warnings for
deprecated APIs and other changes that are needed for React 19. We
recommend upgrading to React 18.3.1 first to help identify any issues
before upgrading to React 19.</p>
</blockquote>
<h2>New Features</h2>
<h3>React</h3>
<ul>
<li>Actions: <code>startTransition</code> can now accept async
functions. Functions passed to <code>startTransition</code> are called
“Actions”. A given Transition can include one or more Actions which
update state in the background and update the UI with one commit. In
addition to updating state, Actions can now perform side effects
including async requests, and the Action will wait for the work to
finish before finishing the Transition. This feature allows Transitions
to include side effects like <code>fetch()</code> in the pending state,
and provides support for error handling, and optimistic updates.</li>
<li><code>useActionState</code>: is a new hook to order Actions inside
of a Transition with access to the state of the action, and the pending
state. It accepts a reducer that can call Actions, and the initial state
used for first render. It also accepts an optional string that is used
if the action is passed to a form <code>action</code> prop to support
progressive enhancement in forms.</li>
<li><code>useOptimistic</code>: is a new hook to update state while a
Transition is in progress. It returns the state, and a set function that
can be called inside a transition to “optimistically” update the state
to expected final value immediately while the Transition completes in
the background. When the transition finishes, the state is updated to
the new value.</li>
<li><code>use</code>: is a new API that allows reading resources in
render. In React 19, <code>use</code> accepts a promise or Context. If
provided a promise, <code>use</code> will suspend until a value is
resolved. <code>use</code> can only be used in render but can be called
conditionally.</li>
<li><code>ref</code> as a prop: Refs can now be used as props, removing
the need for <code>forwardRef</code>.</li>
<li><strong>Suspense sibling pre-warming</strong>: When a component
suspends, React will immediately commit the fallback of the nearest
Suspense boundary, without waiting for the entire sibling tree to
render. After the fallback commits, React will schedule another render
for the suspended siblings to “pre-warm” lazy requests.</li>
</ul>
<h3>React DOM Client</h3>
<ul>
<li><code><form> action</code> prop: Form Actions allow you to
manage forms automatically and integrate with
<code>useFormStatus</code>. When a <code><form> action</code>
succeeds, React will automatically reset the form for uncontrolled
components. The form can be reset manually with the new
<code>requestFormReset</code> API.</li>
<li><code><button> and <input> formAction</code> prop:
Actions can be passed to the <code>formAction</code> prop to configure
form submission behavior. This allows using different Actions depending
on the input.</li>
<li><code>useFormStatus</code>: is a new hook that provides the status
of the parent <code><form> action</code>, as if the form was a
Context provider. The hook returns the values: <code>pending</code>,
<code>data</code>, <code>method</code>, and <code>action</code>.</li>
<li>Support for Document Metadata: We’ve added support for rendering
document metadata tags in components natively. React will automatically
hoist them into the <code><head></code> section of the
document.</li>
<li>Support for Stylesheets: React 19 will ensure stylesheets are
inserted into the <code><head></code> on the client before
revealing the content of a Suspense boundary that depends on that
stylesheet.</li>
<li>Support for async scripts: Async scripts can be rendered anywhere in
the component tree and React will handle ordering and
deduplication.</li>
<li>Support for preloading resources: React 19 ships with
<code>preinit</code>, <code>preload</code>, <code>prefetchDNS</code>,
and <code>preconnect</code> APIs to optimize initial page loads by
moving discovery of additional resources like fonts out of stylesheet
loading. They can also be used to prefetch resources used by an
anticipated navigation.</li>
</ul>
<h3>React DOM Server</h3>
<ul>
<li>Added <code>prerender</code> and <code>prerenderToNodeStream</code>
APIs for static site generation. They are designed to work with
streaming environments like Node.js Streams and Web Streams. Unlike
<code>renderToString</code>, they wait for data to load for HTML
generation.</li>
</ul>
<h3>React Server Components</h3>
<ul>
<li>RSC features such as directives, server components, and server
functions are now stable. This means libraries that ship with Server
Components can now target React 19 as a peer dependency with a
react-server export condition for use in frameworks that support the
Full-stack React Architecture. The underlying APIs used to implement a
React Server Components bundler or framework do not follow semver and
may break between minors in React 19.x. See <a
href="https://19.react.dev/reference/rsc/server-components"
rel="nofollow">docs</a> for how to support React Server Components.</li>
</ul>
<h2>Deprecations</h2>
<ul>
<li>Deprecated: <code>element.ref</code> access: React 19 supports ref
as a prop, so we’re deprecating <code>element.ref</code> in favor of
<code>element.props.ref</code>. Accessing will result in a warning.</li>
<li><code>react-test-renderer</code>: In React 19, react-test-renderer
logs a deprecation warning and has switched to concurrent rendering for
web usage. We recommend migrating your tests to @
testinglibrary.com/docs/react-testing-library/intro/) or @
testingesting-library.com/docs/react-native-testing-library/intro)</li>
</ul>
<h2>Breaking Changes</h2>
<p>React 19 brings in a number of breaking changes, including the
removals of long-deprecated APIs. We recommend first upgrading to
<code>18.3.1</code>, where we've added additional deprecation warnings.
Check out the <a
href="https://19.react.dev/blog/2024/04/25/react-19-upgrade-guide"
rel="nofollow">upgrade guide</a> for more details and guidance on
codemodding.</p>
<h3>React</h3>
<ul>
<li>New JSX Transform is now required: We introduced <a
href="https://legacy.reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html"
rel="nofollow">a new JSX transform</a> in 2020 to improve bundle size
and use JSX without importing React. In React 19, we’re adding
additional improvements like using ref as a prop and JSX speed
improvements that require the new transform.</li>
<li>Errors in render are not re-thrown: Errors that are not caught by an
Error Boundary are now reported to window.reportError. Errors that are
caught by an Error Boundary are reported to console.error. We’ve
introduced <code>onUncaughtError</code> and <code>onCaughtError</code>
methods to <code>createRoot</code> and <code>hydrateRoot</code> to
customize this error handling.</li>
<li>Removed: <code>propTypes</code>: Using <code>propTypes</code> will
now be silently ignored. If required, we recommend migrating to
TypeScript or another type-checking solution.</li>
<li>Removed: <code>defaultProps</code> for functions: ES6 default
parameters can be used in place. Class components continue to support
<code>defaultProps</code> since there is no ES6 alternative.</li>
<li>Removed: <code>contextTypes</code> and <code>getChildContext</code>:
Legacy Context for class components has been removed in favor of the
<code>contextType</code> API.</li>
<li>Removed: string refs: Any usage of string refs need to be migrated
to ref callbacks.</li>
<li>Removed: Module pattern factories: A rarely used pattern that can be
migrated to regular functions.</li>
<li>Removed: <code>React.createFactory</code>: Now that JSX is broadly
supported, all <code>createFactory</code> usage can be migrated to JSX
components.</li>
<li>Removed: <code>react-test-renderer/shallow</code>: This has been a
re-export of <a
href="https://redirect.github.com/enzymejs/react-shallow-renderer">react-shallow-renderer</a>
since React 18. If needed, you can continue to use the third-party
package directly. We recommend using @
testinglibrary.com/docs/react-testing-library/intro/) or @
testingesting-library.com/docs/react-native-testing-library/intro)
instead.</li>
</ul>
<h3>React DOM</h3>
<ul>
<li>Removed: <code>react-dom/test-utils</code>: We’ve moved
<code>act</code> from <code>react-dom/test-utils</code> to react. All
other utilities have been removed.</li>
<li>Removed: <code>ReactDOM</code>.<code>render</code>,
<code>ReactDOM</code>.<code>hydrate</code>: These have been removed in
favor of the concurrent equivalents:
<code>ReactDOM</code>.<code>createRoot</code> and
<code>ReactDOM.hydrateRoot</code>.</li>
<li>Removed: <code>unmountComponentAtNode</code>: Removed in favor of
<code>root.unmount()</code>.</li>
<li>Removed: <code>ReactDOM</code>.<code>findDOMNode</code>: You can
replace <code>ReactDOM</code>.<code>findDOMNode</code> with DOM
Refs.</li>
</ul>
<h2>Notable Changes</h2>
<h3>React</h3>
<ul>
<li><code><Context></code> as a provider: You can now render
<code><Context></code> as a provider instead of
<code><Context.Provider></code>.</li>
<li>Cleanup functions for refs: When the component unmounts, React will
call the cleanup function returned from the ref callback.</li>
<li><code>useDeferredValue</code> initial value argument: When provided,
<code>useDeferredValue</code> will return the initial value for the
initial render of a component, then schedule a re-render in the
background with the <code>deferredValue</code> returned.</li>
<li>Support for Custom Elements: React 19 now passes all tests on <a
href="https://custom-elements-everywhere.com/" rel="nofollow">Custom
Elements Everywhere</a>.</li>
<li>StrictMode changes: <code>useMemo</code> and
<code>useCallback</code> will now reuse the memoized results from the
first render, during the second render. Additionally, StrictMode will
now double-invoke ref callback functions on initial mount.</li>
<li>UMD builds removed: To load React 19 with a script tag, we recommend
using an ESM-based CDN such as <a href="http://esm.sh"
rel="nofollow">esm.sh</a>.</li>
</ul>
<h3>React DOM</h3>
<ul>
<li>Diffs for hydration errors: In the case of a mismatch, React 19 logs
a single error with a diff of the mismatched content.</li>
<li>Compatibility with third-party scripts and extensions: React will
now force a client re-render to fix up any mismatched content caused by
elements inserted by third-party JS.</li>
</ul>
<h2>TypeScript Changes</h2>
<p>The most common changes can be codemodded with <code>npx
types-react-codemod@latest preset-19
./path-to-your-react-ts-files</code>.</p>
<ul>
<li>Removed deprecated TypeScript types:
<ul>
<li><code>ReactChild</code> (replacement: <code>React.ReactElement |
number | string)</code></li>
<li><code>ReactFragment</code> (replacement:
<code>Iterable<React.ReactNode></code>)</li>
<li><code>ReactNodeArray</code> (replacement:
<code>ReadonlyArray<React.ReactNode></code>)</li>
<li><code>ReactText</code> (replacement: <code>number |
string</code>)</li>
<li><code>VoidFunctionComponent</code> (replacement:
<code>FunctionComponent</code>)</li>
<li><code>VFC</code> (replacement: <code>FC</code>)</li>
<li>Moved to <code>prop-types</code>: <code>Requireable</code>,
<code>ValidationMap</code>, <code>Validator</code>,
<code>WeakValidationMap</code></li>
<li>Moved to <code>create-react-class</code>:
<code>ClassicComponentClass</code>, <code>ClassicComponent</code>,
<code>ClassicElement</code>, <code>ComponentSpec</code>,
<code>Mixin</code>, <code>ReactChildren</code>, <code>ReactHTML</code>,
<code>ReactSVG</code>, <code>SFCFactory</code></li>
</ul>
</li>
<li>Disallow implicit return in refs: refs can now accept cleanup
functions. When you return something else, we can’t tell if you
intentionally returned something not meant to clean up or returned the
wrong value. Implicit returns of anything but functions will now
error.</li>
<li>Require initial argument to <code>useRef</code>: The initial
argument is now required to match <code>useState</code>,
<code>createContext</code> etc</li>
<li>Refs are mutable by default: Ref objects returned from
<code>useRef()</code> are now always mutable instead of sometimes being
immutable. This feature was too confusing for users and conflicted with
legit cases where refs were managed by React and manually written
to.</li>
<li>Strict <code>ReactElement</code> typing: The props of React elements
now default to <code>unknown</code> instead of <code>any</code> if the
element is typed as <code>ReactElement</code></li>
<li>JSX namespace in TypeScript: The global <code>JSX</code> namespace
is removed to improve interoperability with other libraries using JSX.
Instead, the JSX namespace is available from the React package:
<code>import { JSX } from 'react'</code></li>
<li>Better <code>useReducer</code> typings: Most <code>useReducer</code>
usage should not require explicit type arguments.<br>
For example,
<div class="highlight highlight-source-diff notranslate
position-relative overflow-auto"
data-snippet-clipboard-copy-content="-useReducer<React.Reducer<State,
Action>>(reducer)
+useReducer(reducer) "><pre><span class="pl-md"><span
class="pl-md">-</span>useReducer<React.Reducer<State,
Action>>(reducer) </span>
<span class="pl-mi1"><span class="pl-mi1">+</span>useReducer(reducer)
</span></pre></div>
or
<div class="highlight highlight-source-diff notranslate
position-relative overflow-auto"
data-snippet-clipboard-copy-content="-useReducer<React.Reducer<State,
Action>>(reducer)
+useReducer<State, [Action]>(reducer)"><pre><span
class="pl-md"><span
class="pl-md">-</span>useReducer<React.Reducer<State,
Action>>(reducer) </span>
<span class="pl-mi1"><span class="pl-mi1">+</span>useReducer<State,
[Action]>(reducer)</span></pre></div>
</li>
</ul>
<h2>All Changes</h2>
<h3>React</h3>
<ul>
<li>Add support for async Actions (<a
href="https://redirect.github.com/facebook/react/pull/26621"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26621/hovercard">#26621</a>, <a
href="https://redirect.github.com/facebook/react/pull/26726"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26726/hovercard">#26726</a>, <a
href="https://redirect.github.com/facebook/react/pull/28078"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28078/hovercard">#28078</a>, <a
href="https://redirect.github.com/facebook/react/pull/28097"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28097/hovercard">#28097</a>, <a
href="https://redirect.github.com/facebook/react/pull/29226"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29226/hovercard">#29226</a>, <a
href="https://redirect.github.com/facebook/react/pull/29618"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29618/hovercard">#29618</a>, <a
href="https://redirect.github.com/facebook/react/pull/29670"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29670/hovercard">#29670</a>, <a
href="https://redirect.github.com/facebook/react/pull/26716"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26716/hovercard">#26716</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a> and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sebmarkbage/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sebmarkbage">@ sebmarkbage</a>)</li>
<li>Add <code>useActionState()</code> hook to update state based on the
result of a Form Action (<a
href="https://redirect.github.com/facebook/react/pull/27270"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27270/hovercard">#27270</a>, <a
href="https://redirect.github.com/facebook/react/pull/27278"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27278/hovercard">#27278</a>, <a
href="https://redirect.github.com/facebook/react/pull/27309"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27309/hovercard">#27309</a>, <a
href="https://redirect.github.com/facebook/react/pull/27302"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27302/hovercard">#27302</a>, <a
href="https://redirect.github.com/facebook/react/pull/27307"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27307/hovercard">#27307</a>, <a
href="https://redirect.github.com/facebook/react/pull/27366"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27366/hovercard">#27366</a>, <a
href="https://redirect.github.com/facebook/react/pull/27370"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27370/hovercard">#27370</a>, <a
href="https://redirect.github.com/facebook/react/pull/27321"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27321/hovercard">#27321</a>, <a
href="https://redirect.github.com/facebook/react/pull/27374"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27374/hovercard">#27374</a>, <a
href="https://redirect.github.com/facebook/react/pull/27372"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27372/hovercard">#27372</a>, <a
href="https://redirect.github.com/facebook/react/pull/27397"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27397/hovercard">#27397</a>, <a
href="https://redirect.github.com/facebook/react/pull/27399"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27399/hovercard">#27399</a>, <a
href="https://redirect.github.com/facebook/react/pull/27460"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27460/hovercard">#27460</a>, <a
href="https://redirect.github.com/facebook/react/pull/28557"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28557/hovercard">#28557</a>, <a
href="https://redirect.github.com/facebook/react/pull/27570"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27570/hovercard">#27570</a>, <a
href="https://redirect.github.com/facebook/react/pull/27571"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27571/hovercard">#27571</a>, <a
href="https://redirect.github.com/facebook/react/pull/28631"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28631/hovercard">#28631</a>, <a
href="https://redirect.github.com/facebook/react/pull/28788"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28788/hovercard">#28788</a>, <a
href="https://redirect.github.com/facebook/react/pull/29694"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29694/hovercard">#29694</a>, <a
href="https://redirect.github.com/facebook/react/pull/29695"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29695/hovercard">#29695</a>, <a
href="https://redirect.github.com/facebook/react/pull/29694"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29694/hovercard">#29694</a>, <a
href="https://redirect.github.com/facebook/react/pull/29665"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/29665/hovercard">#29665</a>, <a
href="https://redirect.github.com/facebook/react/pull/28232"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28232/hovercard">#28232</a>, <a
href="https://redirect.github.com/facebook/react/pull/28319"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28319/hovercard">#28319</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/eps1lon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/eps1lon">@ eps1lon</a>, and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/rickhanlonii/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/rickhanlonii">@ rickhanlonii</a>)</li>
<li>Add <code>use()</code> API to read resources in render (<a
href="https://redirect.github.com/facebook/react/pull/25084"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25084/hovercard">#25084</a>, <a
href="https://redirect.github.com/facebook/react/pull/25202"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25202/hovercard">#25202</a>, <a
href="https://redirect.github.com/facebook/react/pull/25207"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25207/hovercard">#25207</a>, <a
href="https://redirect.github.com/facebook/react/pull/25214"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25214/hovercard">#25214</a>, <a
href="https://redirect.github.com/facebook/react/pull/25226"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25226/hovercard">#25226</a>, <a
href="https://redirect.github.com/facebook/react/pull/25247"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25247/hovercard">#25247</a>, <a
href="https://redirect.github.com/facebook/react/pull/25539"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25539/hovercard">#25539</a>, <a
href="https://redirect.github.com/facebook/react/pull/25538"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25538/hovercard">#25538</a>, <a
href="https://redirect.github.com/facebook/react/pull/25537"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25537/hovercard">#25537</a>, <a
href="https://redirect.github.com/facebook/react/pull/25543"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25543/hovercard">#25543</a>, <a
href="https://redirect.github.com/facebook/react/pull/25561"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25561/hovercard">#25561</a>, <a
href="https://redirect.github.com/facebook/react/pull/25620"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25620/hovercard">#25620</a>, <a
href="https://redirect.github.com/facebook/react/pull/25615"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25615/hovercard">#25615</a>, <a
href="https://redirect.github.com/facebook/react/pull/25922"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25922/hovercard">#25922</a>, <a
href="https://redirect.github.com/facebook/react/pull/25641"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25641/hovercard">#25641</a>, <a
href="https://redirect.github.com/facebook/react/pull/25634"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25634/hovercard">#25634</a>, <a
href="https://redirect.github.com/facebook/react/pull/26232"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26232/hovercard">#26232</a>, <a
href="https://redirect.github.com/facebook/react/pull/26535"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26535/hovercard">#26536</a>, <a
href="https://redirect.github.com/facebook/react/pull/26739"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26739/hovercard">#26739</a>, <a
href="https://redirect.github.com/facebook/react/pull/28233"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28233/hovercard">#28233</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/mofeiZ/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/mofeiZ">@ mofeiZ</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sebmarkbage/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sebmarkbage">@ sebmarkbage</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sophiebits/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sophiebits">@ sophiebits</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/eps1lon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/eps1lon">@ eps1lon</a>, and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/hansottowirtz/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/hansottowirtz">@
hansottowirtz</a>)</li>
<li>Add <code>useOptimistic()</code> hook to display mutated state
optimistically during an async mutation (<a
href="https://redirect.github.com/facebook/react/pull/26740"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26740/hovercard">#26740</a>, <a
href="https://redirect.github.com/facebook/react/pull/26772"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26772/hovercard">#26772</a>, <a
href="https://redirect.github.com/facebook/react/pull/27277"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27277/hovercard">#27277</a>, <a
href="https://redirect.github.com/facebook/react/pull/27453"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27453/hovercard">#27453</a>, <a
href="https://redirect.github.com/facebook/react/pull/27454"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27454/hovercard">#27454</a>, <a
href="https://redirect.github.com/facebook/react/pull/27936"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27936/hovercard">#27936</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Added an <code>initialValue</code> argument to
<code>useDeferredValue()</code> hook (<a
href="https://redirect.github.com/facebook/react/pull/27500"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27500/hovercard">#27500</a>, <a
href="https://redirect.github.com/facebook/react/pull/27509"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27509/hovercard">#27509</a>, <a
href="https://redirect.github.com/facebook/react/pull/27512"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27512/hovercard">#27512</a>, <a
href="https://redirect.github.com/facebook/react/pull/27888"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27888/hovercard">#27888</a>, <a
href="https://redirect.github.com/facebook/react/pull/27550"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27550/hovercard">#27550</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Support refs as props, warn on <code>element.ref</code> access (<a
href="https://redirect.github.com/facebook/react/pull/28348"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28348/hovercard">#28348</a>, <a
href="https://redirect.github.com/facebook/react/pull/28464"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28464/hovercard">#28464</a>, <a
href="https://redirect.github.com/facebook/react/pull/28731"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28731/hovercard">#28731</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Support Custom Elements (<a
href="https://redirect.github.com/facebook/react/pull/22184"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/22184/hovercard">#22184</a>, <a
href="https://redirect.github.com/facebook/react/pull/26524"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26524/hovercard">#26524</a>, <a
href="https://redirect.github.com/facebook/react/pull/26523"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26523/hovercard">#26523</a>, <a
href="https://redirect.github.com/facebook/react/pull/27511"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27511/hovercard">#27511</a>, <a
href="https://redirect.github.com/facebook/react/pull/24541"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/24541/hovercard">#24541</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/josepharhar/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/josepharhar">@ josepharhar</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sebmarkbage/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sebmarkbage">@ sebmarkbage</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/gnoff/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/gnoff">@ gnoff</a> and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/eps1lon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/eps1lon">@ eps1lon</a>)</li>
<li>Add ref cleanup function (<a
href="https://redirect.github.com/facebook/react/pull/25686"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25686/hovercard">#25686</a>, <a
href="https://redirect.github.com/facebook/react/pull/28883"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28883/hovercard">#28883</a>, <a
href="https://redirect.github.com/facebook/react/pull/28910"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28910/hovercard">#28910</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sammy-SC/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sammy-SC">@ sammy-SC</a>), <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/jackpope/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/jackpope">@ jackpope</a>, and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/kassens/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/kassens">@ kassens</a>)</li>
<li>Sibling pre-rendering replaced by sibling pre-warming (<a
href="https://redirect.github.com/facebook/react/pull/26380"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26380/hovercard">#26380</a>, <a
href="https://redirect.github.com/facebook/react/pull/26549"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26549/hovercard">#26549</a>, <a
href="https://redirect.github.com/facebook/react/pull/30761"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30761/hovercard">#30761</a>, <a
href="https://redirect.github.com/facebook/react/pull/30800"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30800/hovercard">#30800</a>, <a
href="https://redirect.github.com/facebook/react/pull/30762"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30762/hovercard">#30762</a>, <a
href="https://redirect.github.com/facebook/react/pull/30879"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30879/hovercard">#30879</a>, <a
href="https://redirect.github.com/facebook/react/pull/30934"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30934/hovercard">#30934</a>, <a
href="https://redirect.github.com/facebook/react/pull/30952"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/30952/hovercard">#30952</a>, <a
href="https://redirect.github.com/facebook/react/pull/31056"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31056/hovercard">#31056</a>, <a
href="https://redirect.github.com/facebook/react/pull/31452"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/31452/hovercard">#31452</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sammy-SC/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sammy-SC">@ sammy-SC</a>), <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/gnoff/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/gnoff">@ gnoff</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/jackpope/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/jackpope">@ jackpope</a>, <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/rickhanlonii/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/rickhanlonii">@ rickhanlonii</a>)</li>
<li>Don’t rethrow errors at the root (<a
href="https://redirect.github.com/facebook/react/pull/28627"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28627/hovercard">#28627</a>, <a
href="https://redirect.github.com/facebook/react/pull/28641"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28641/hovercard">#28641</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sebmarkbage/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sebmarkbage">@ sebmarkbage</a>)</li>
<li>Batch sync discrete, continuous, and default lanes (<a
href="https://redirect.github.com/facebook/react/pull/25700"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25700/hovercard">#25700</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/tyao1/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/tyao1">@ tyao1</a>)</li>
<li>Switch <code><Context></code> to mean
<code><Context.Provider></code> (<a
href="https://redirect.github.com/facebook/react/pull/28226"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28226/hovercard">#28226</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/gaearon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/gaearon">@ gaearon</a>)</li>
<li>Changes to <em>StrictMode</em>
<ul>
<li>Handle <code>info</code>, <code>group</code>, and
<code>groupCollapsed</code> in <em>StrictMode</em> logging (<a
href="https://redirect.github.com/facebook/react/pull/25172"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25172/hovercard">#25172</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/timneutkens/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/timneutkens">@ timneutkens</a>)</li>
<li>Refs are now attached/detached/attached in <em>StrictMode</em> (<a
href="https://redirect.github.com/facebook/react/pull/25049"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25049/hovercard">#25049</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sammy-SC/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sammy-SC">@ sammy-SC</a>)</li>
<li>Fix <code>useSyncExternalStore()</code> hydration in
<em>StrictMode</em> (<a
href="https://redirect.github.com/facebook/react/pull/26791"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26791/hovercard">#26791</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sophiebits/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sophiebits">@ sophiebits</a>)</li>
<li>Always trigger <code>componentWillUnmount()</code> in
<em>StrictMode</em> (<a
href="https://redirect.github.com/facebook/react/pull/26842"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26842/hovercard">#26842</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/tyao1/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/tyao1">@ tyao1</a>)</li>
<li>Restore double invoking <code>useState()</code> and
<code>useReducer()</code> initializer functions in <em>StrictMode</em>
(<a href="https://redirect.github.com/facebook/react/pull/28248"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/28248/hovercard">#28248</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/eps1lon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/eps1lon">@ eps1lon</a>)</li>
<li>Reuse memoized result from first pass (<a
href="https://redirect.github.com/facebook/react/pull/25583"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25583/hovercard">#25583</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Fix <code>useId()</code> in <em>StrictMode</em> (<a
href="https://redirect.github.com/facebook/react/pull/25713"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25713/hovercard">#25713</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/gnoff/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/gnoff">@ gnoff</a>)</li>
<li>Add component name to <em>StrictMode</em> error messages (<a
href="https://redirect.github.com/facebook/react/pull/25718"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25718/hovercard">#25718</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sammy-SC/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sammy-SC">@ sammy-SC</a>)</li>
</ul>
</li>
<li>Add support for rendering BigInt (<a
href="https://redirect.github.com/facebook/react/pull/24580"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/24580/hovercard">#24580</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/eps1lon/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/eps1lon">@ eps1lon</a>)</li>
<li><code>act()</code> no longer checks <code>shouldYield</code> which
can be inaccurate in test environments (<a
href="https://redirect.github.com/facebook/react/pull/26317"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26317/hovercard">#26317</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Warn when keys are spread with props (<a
href="https://redirect.github.com/facebook/react/pull/25697"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25697/hovercard">#25697</a>, <a
href="https://redirect.github.com/facebook/react/pull/26080"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26080/hovercard">#26080</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/sebmarkbage/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/sebmarkbage">@ sebmarkbage</a> and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/kassens/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/kassens">@ kassens</a>)</li>
<li>Generate sourcemaps for production build artifacts (<a
href="https://redirect.github.com/facebook/react/pull/26446"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26446/hovercard">#26446</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/markerikson/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/markerikson">@ markerikson</a>)</li>
<li>Improve stack diffing algorithm (<a
href="https://redirect.github.com/facebook/react/pull/27132"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/27132/hovercard">#27132</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/KarimP/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/KarimP">@ KarimP</a>)</li>
<li>Suspense throttling lowered from 500ms to 300ms (<a
href="https://redirect.github.com/facebook/react/pull/26803"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26803/hovercard">#26803</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Lazily propagate context changes (<a
href="https://redirect.github.com/facebook/react/pull/20890"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/20890/hovercard">#20890</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a> and <a
class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/gnoff/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/gnoff">@ gnoff</a>)</li>
<li>Immediately rerender pinged fiber (<a
href="https://redirect.github.com/facebook/react/pull/25074"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/25074/hovercard">#25074</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Move update scheduling to microtask (<a
href="https://redirect.github.com/facebook/react/pull/26512"
data-hovercard-type="pull_request"
data-hovercard-url="/facebook/react/pull/26512/hovercard">#26512</a> by
<a class="user-mention notranslate" data-hovercard-type="user"
data-hovercard-url="/users/acdlite/hovercard"
data-octo-click="hovercard-link-click"
data-octo-dimensions="link_type:self"
href="https://redirect.github.com/acdlite">@ acdlite</a>)</li>
<li>Consistently apply throttled retries (<a
href="https://redirect.github.com/facebook/react/pull/26611"
data-hovercard-typ…
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Stacked on top of #28498 for test fixes.
Don't Rethrow
When we started React it was 1:1 setState calls a series of renders and if they error, it errors where the setState was called. Simple. However, then batching came and the error actually got thrown somewhere else. With concurrent mode, it's not even possible to get setState itself to throw anymore.
In fact, all APIs that can rethrow out of React are executed either at the root of the scheduler or inside a DOM event handler.
If you throw inside a React.startTransition callback that's sync, then that will bubble out of the startTransition but if you throw inside an async callback or a useTransition we now need to handle it at the hook site. So in 19 we need to make all React.startTransition swallow the error (and report them to reportError).
The only one remaining that can throw is flushSync but it doesn't really make sense for it to throw at the callsite neither because batching. Just because something rendered in this flush doesn't mean it was rendered due to what was just scheduled and doesn't mean that it should abort any of the remaining code afterwards. setState is fire and forget. It's send an instruction elsewhere, it's not part of the current imperative code.
Error boundaries never rethrow. Since you should really always have error boundaries, most of the time, it wouldn't rethrow anyway.
Rethrowing also actually currently drops errors on the floor since we can only rethrow the first error, so to avoid that we'd need to call reportError anyway. This happens in RN events.
The other issue with rethrowing is that it logs an extra console.error. Since we're not sure that user code will actually log it anywhere we still log it too just like we do with errors inside error boundaries which leads all of these to log twice.
The goal of this PR is to never rethrow out of React instead, errors outside of error boundaries get logged to reportError. Event system errors too.
Breaking Changes
The main thing this affects is testing where you want to inspect the errors thrown. To make it easier to port, if you're inside
actwe track the error into act in an aggregate error and then rethrow it at the root ofact. Unlike before though, if you flush synchronously inside of act it'll still continue until the end of act before rethrowing.I expect most user code breakages would be to migrate from
flushSynctoactif you assert on throwing.However, in the React repo we also have
internalActand thewaitForThrowhelpers. Since these have to use public production implementations we track these using the global onerror or process uncaughtException. Unlike regular act, includes both event handler errors and onRecoverableError by default too. Not just render/commit errors. So I had to account for that in our tests.We restore logging an extra log for uncaught errors after the main log with the component stack in it. We use
console.warn. This is not yet ignorable if you preventDefault to the main error event. To avoid confusion if you don't end up logging the error to console I just addedAn error occurred.Polyfill
All browsers we support really supports
reportErrorbut not all test and server environments do, so I implemented a polyfill for browser and node inshared/reportGlobalError. I don't love that this is included in all builds and gets duplicated into isomorphic even though it's not actually needed in production. Maybe in the future we can require a polyfill for this.Follow Ups
In a follow up, I'll make caught vs uncaught error handling be configurable too.