We're currently hardcoding experimental options to
`eslint-plugin-react-hooks`. This blocks the release on features that
might not be ready.
This PR extends the ReactFeatureFlag infra to support flags for
`eslint-plugin-react-hooks`. An alternative would be to create a
separate flag system for build tools, but for now we have a small number
of these and reusing existing infra seems like the simplest approach.
I ran a full `yarn build` and checked the output resolved the flag
values as expected:
_build/oss-stable-semver/eslint-plugin-react-hooks/cjs/eslint-plugin-react-hooks.development.js_
```js
var eprh_enableUseKeyedStateCompilerLint = false;
var eprh_enableVerboseNoSetStateInEffectCompilerLint = false;
var eprh_enableExhaustiveEffectDependenciesCompilerLint = 'off';
```
_build/facebook-www/ESLintPluginReactHooks-dev.classic.js_
```js
var eprh_enableUseKeyedStateCompilerLint = true;
var eprh_enableVerboseNoSetStateInEffectCompilerLint = true;
var eprh_enableExhaustiveEffectDependenciesCompilerLint = 'extra-only';
```
---------
Co-authored-by: lauren <lauren@anysphere.co>
## Summary
Enables Basic View Transition support for React Native Fabric renderer.
**Implemented:**
- Added FabricUIManager bindings for view transition methods:
`applyViewTransitionName`, `startViewTransition`
- Implemented `startViewTransition` with proper callback orchestration
(mutation → layout → afterMutation → spawnedWork → passive)
- Added fallback behavior that flushes work synchronously when Fabric's
`startViewTransition` returns null (e.g., when the ViewTransition
ReactNativeFeatureFlag is not enabled)
- Added Flow type declarations for new FabricUIManager methods
- Stubbed with `__DEV__` warnings for all the other view transition
config functions that are not yet implemented
This allows React Native apps using Fabric to leverage the View
Transition API for coordinated animations during state transitions, with
graceful degradation when the native side doesn't support it.
Below are diagrams of proposed architecture in fabric, and observation
of what/when config functions get called during a basic shared
transition example
<img width="2290" height="1529" alt="Untitled-2026-03-19-1240"
src="https://github.com/user-attachments/assets/192c9169-bc25-449c-a33b-dfec67179e7f"
/>
## How did you test this change?
- [x] `yarn flow fabric` - Flow type checks pass
- [x] `yarn lint` - Lint checks pass
- [x] Manually tested in Android catalyst app with
`enableViewTransition` and `enableViewTransitionForPersistenceMode `in
`ReactFeatureFlags.test-renderer.native-fb.js` and View Transition
enabled via ReactNativeFeatureFlag
- [x] Verified in the minified `ReactFabric-dev.fb.js` that the 'shim'
config functions are not included
- [x] Verified fallback behavior logs warning in `__DEV__` and flushes
work synchronously when ViewTransition flag isn't enabled in Fabric
## Summary
This flag enables React's integration with the browser [Trusted Types
API](https://developer.mozilla.org/en-US/docs/Web/API/Trusted_Types_API).
The Trusted Types API is a browser security feature that helps prevent
DOM-based XSS attacks. When a site enables Trusted Types enforcement via
`Content-Security-Policy: require-trusted-types-for 'script'`, the
browser requires that values passed to DOM injection sinks (like
`innerHTML`) are typed objects (`TrustedHTML`, `TrustedScript`,
`TrustedScriptURL`) created through developer-defined sanitization
policies, rather than raw strings.
### What changed
Previously, React always coerced values to strings (via `'' + value`)
before passing them to DOM APIs like `setAttribute` and `innerHTML`.
This broke Trusted Types because it converted typed objects into plain
strings, which the browser would then reject under Trusted Types
enforcement.
React now passes values directly to DOM APIs without string coercion,
preserving Trusted Types objects so the browser can validate them. This
applies to `dangerouslySetInnerHTML`, all HTML and SVG attributes, and
URL attributes (`href`, `action`, etc).
### Before (broken)
Using Trusted Types with something like`dangerouslySetInnerHTML` would
throw:
```js
const sanitizer = trustedTypes.createPolicy('sanitizer', {
createHTML: (input) => DOMPurify.sanitize(input),
});
function Comment({text}) {
const clean = sanitizer.createHTML(text);
// clean is a TrustedHTML object, but React would call '' + clean,
// converting it back to a plain string before setting innerHTML.
// Under Trusted Types enforcement, the browser rejects the string:
//
// TypeError: Failed to set 'innerHTML' on 'Element':
// This document requires 'TrustedHTML' assignment.
return <div dangerouslySetInnerHTML={{__html: clean}} />;
}
```
### After (works)
React now passes the TrustedHTML object directly to the DOM without
stringifying it:
```js
const policy = trustedTypes.createPolicy('sanitizer', {
createHTML: (input) => DOMPurify.sanitize(input),
});
function Comment({text}) {
// TrustedHTML objects are passed directly to innerHTML
return <div dangerouslySetInnerHTML={{__html: policy.createHTML(text)}} />;
}
function UserProfile({bio}) {
// String attribute values also preserve Trusted Types objects
return <div data-bio={policy.createHTML(bio)} />;
}
```
## Non-breaking change
- Sites using Trusted Types: React no longer breaks Trusted Types enforcement. TrustedHTML and TrustedScriptURL objects passed through React props are forwarded to the DOM without being stringified.
- Sites not using Trusted Types: No behavior change. DOM APIs accept both strings and Trusted Types objects, so removing the explicit string coercion is functionally identical.
Small optimization for useEffectEvent. Not sure we even need a flag for
it, but it will be a nice killswitch.
As an added benefit, it fixes a bug when `enableViewTransition` is on,
where we were not updating the useEffectEvent callback when a tree went
from hidden to visible.
## Overview
Adds a feature flag `enableParallelTransitions` to experiment with
engantling transitions less often.
## Motivation
Currently we over-entangle transition lanes.
It's a common misunderstanding that React entangles all transitions,
always. We actually will complete transitions independently in many
cases. For example, [this
codepen](https://codepen.io/GabbeV/pen/pvyKBrM) from
[@gabbev](https://bsky.app/profile/gabbev.bsky.social/post/3m6uq2abihk2x)
shows transitions completing independently.
However, in many cases we entangle when we don't need to, instead of
letting the independent transitons complete independently. We still want
to entangle for updates that happen on the same queue.
## Example
As an example of what this flag would change, consider two independent
counter components:
```js
function Counter({ label }) {
const [count, setCount] = useState(0);
return (
<div>
<span>{use(readCache(`${label} ${count}`))} </span>
<Button
action={() => {
setCount((c) => c + 1);
}}
>
Next {label}
</Button>
</div>
);
}
```
```js
export default function App() {
return (
<>
<Counter label="A" />
<Counter label="B" />
</>
);
}
```
### Before
The behavior today is to entange them, meaning they always commit
together:
https://github.com/user-attachments/assets/adead60e-8a98-4a20-a440-1efdf85b2142
### After
In this experiment, they will complete independently (if they don't
depend on each other):
https://github.com/user-attachments/assets/181632b5-3c92-4a29-a571-3637f3fab8cd
## Early Research
This change is in early research, and is not in the experimental
channel. We're going to experiment with this at Meta to understand how
much of a breaking change, and how beneficial it is before commiting to
shipping it in experimental and beyond.
This PR adds text node support to FragmentInstance operations, allowing
fragment refs to properly handle fragments that contain text nodes
(either mixed with elements or text-only).
Not currently adding/removing new text nodes as we don't need to track
them for events or observers in DOM. Will follow up on this and with
Fabric support.
## Support through parent element
- `dispatchEvent`
- `compareDocumentPosition`
- `getRootNode`
## Support through Range API
- `getClientRects`: Uses Range to calculate bounding rects for text
nodes
- `scrollIntoView`: Uses Range to scroll to text node positions directly
## No support
- `focus`/`focusLast`/`blur`: Noop for text-only fragments
- `observeUsing`: Warns for text-only fragments in DEV
- `addEventListener`/`removeEventListener`: Ignores text nodes, but
still works on Fragment level through `dispatchEvent`
Follow-up to https://github.com/facebook/react/pull/34665.
Already gated on `enableProfilerTimer` everywhere, which is only enabled
for `__PROFILE__`, except for Flight should be unified in a future.
When dealing with optimistic state, a common problem is not knowing the
id of the thing we're waiting on. Items in lists need keys (and single
items should often have keys too to reset their state). As a result you
have to generate fake keys. It's a pain to manage those and when the
real item comes in, you often end up rendering that with a different
`key` which resets the state of the component tree. That in turns works
against the grain of React and a lot of negatives fall out of it.
This adds a special `optimisticKey` symbol that can be used in place of
a `string` key.
```js
import {optimisticKey} from 'react';
...
const [optimisticItems, setOptimisticItems] = useOptimistic([]);
const children = savedItems.concat(
optimisticItems.map(item =>
<Item key={optimisticKey} item={item} />
)
);
return <div>{children}</div>;
```
The semantics of this `optimisticKey` is that the assumption is that the
newly saved item will be rendered in the same slot as the previous
optimistic items. State is transferred into whatever real key ends up in
the same slot.
This might lead to some incorrect transferring of state in some cases
where things don't end up lining up - but it's worth it for simplicity
in many cases since dealing with true matching of optimistic state is
often very complex for something that only lasts a blink of an eye.
If a new item matches a `key` elsewhere in the set, then that's favored
over reconciling against the old slot.
One quirk with the current algorithm is if the `savedItems` has items
removed, then the slots won't line up by index anymore and will be
skewed. We might be able to add something where the optimistic set is
always reconciled against the end. However, it's probably better to just
assume that the set will line up perfectly and otherwise it's just best
effort that can lead to weird artifacts.
An `optimisticKey` will match itself for updates to the same slot, but
it will not match any existing slot that is not an `optimisticKey`. So
it's not an `any`, which I originally called it, because it doesn't
match existing real keys against new optimistic keys. Only one
direction.
We already append `randomKey` to each handle name to prevent external
libraries from accessing and relying on these internals. But more
libraries recently have been getting around this by simply iterating
over the element properties and using a `startsWith` check.
This flag allows us to experiment with moving these handles to an
internal map.
This PR starts with the two most common internals, the props object and
the fiber. We can consider moving additional properties such as the
container root and others depending on perf results.
This PR adds a `unstable_reactFragments?: Set<FragmentInstance>`
property to DOM nodes that belong to a Fragment with a ref (top level
host components). This allows you to access a FragmentInstance from a
DOM node.
This is flagged behind `enableFragmentRefsInstanceHandles`.
The primary use case to unblock is reusing IntersectionObserver
instances. A fairly common practice is to cache and reuse
IntersectionObservers that share the same config, with a map of
node->callbacks to run for each entry in the IO callback. Currently this
is not possible with Fragment Ref `observeUsing` because the key in the
cache would have to be the `FragmentInstance` and you can't find it
without a handle from the node. This works now by accessing
`entry.target.fragments`.
This also opens up possibilities to use `FragmentInstance` operations in
other places, such as events. We can do
`event.target.unstable_reactFragments`, then access
`fragmentInstance.getClientRects` for example. In a future PR, we can
assign an event's `currentTarget` as the Fragment Ref for a more direct
handle when the event has been dispatched by the Fragment itself.
The first commit here implemented a handle only on observed elements.
This is awkward because there isn't a good way to document or expose
this temporary property. `element.fragments` is closer to what we would
expect from a DOM API if a standard was implemented here. And by
assigning it to all top-level nodes of a Fragment, it can be used beyond
the cached IntersectionObserver callback.
One tradeoff here is adding extra work during the creation of
FragmentInstances as well as keeping track of adding/removing nodes.
Previously we only track the Fiber on creation but here we add a
traversal which could apply to a large set of top-level host children.
The `element.unstable_reactFragments` Set can also be randomly ordered.
## Summary
Experimentation has completed for this at Meta and we've observed
positive impact on key React Native surfaces.
## How did you test this change?
yarn flow fabric
This adds `experimental_scrollIntoView(alignToTop)`. It doesn't yet
support `scrollIntoView(options)`.
Cases:
- No host children: Without host children, we represent the virtual
space of the Fragment by attempting to scroll to the nearest edge by
using its siblings. If the preferred sibling is not found, we'll try the
other side, and then the parent.
- 1 or more host children: In order to handle the case of children
spread between multiple scroll containers, we scroll to each child in
reverse order based on the `alignToTop` flag.
Due to the complexity of multiple scroll containers and dealing with
portals, I've added this under a separate feature flag with an
experimental prefix. We may stabilize it along with the other APIs, but
this allows us to not block the whole feature on it.
This PR was previously implementing a much more complex approach to
handling multiple scroll containers and portals. We're going to start
with the simple loop and see if we can find any concrete use cases where
that doesn't suffice. 01f31d43013ba7f6f54fd8a36990bbafc3c3cc68 is the
diff between approaches here.
After an easy couple version with #34252, this version is less flexible
(and safer) on inferring exported types mainly.
We require to annotate some exported types to differentiate between
`boolean` and literal `true` types, etc.
## Summary
Make this flag dynamic, so it can be controlled internally.
## How did you test this change?
Build, observe that `console.timeStamp` is only present in FB artifacts
and `enableComponentPerformanceTrack` is referenced.
## Summary
We completed testing on these internally, so can cleanup the separate
fast and slow paths and remove the `enableShallowPropDiffing` flag which
we're not pursuing.
## How did you test this change?
```
yarn test ReactNativeAttributePayloadFabric
```
Enabled in experimental channel.
We know this is critical semantics to enforce at the HTML level since if
you don't then you can't add explicit boundaries after the fact.
However, this might have to go in a major release to allow for
upgrading.
This fixes a long standing issue that controlled inputs gets out of sync
with the browser state if it's changed before we hydrate.
This resolves the issue by replaying the change events (click, input and
change) if the value has changed by the time we commit the hydration.
That way you can reflect the new value in state to bring it in sync. It
does this whether controlled or uncontrolled.
The idea is that this should be ok to replay because it's similar to the
continuous events in that it doesn't replay a sequence but only reflects
the current state of the tree.
Since this is a breaking change I added it behind
`enableHydrationChangeEvent` flag.
There is still an additional issue remaining that I intend to address in
a follow up. If a `useLayoutEffect` triggers an sync rerender on
hydration (always a bad idea) then that can rerender before we have had
a chance to replay the change events. If that renders through a input
then that input will always override the browser value with the
controlled value. Which will reset it before we've had a change to
update to the new value.
Adds Fragment Ref support to RN through the Fabric config, starting with
`observeUsing`/`unobserveUsing`. This is mostly a copy from the
implementation on DOM, and some of it can likely be shared in the future
but keeping it separate for now and we can refactor as we add more
features.
Added a basic test with Fabric, but testing specific methods requires so
much mocking that it doesn't seem valuable here.
I built Fabric and ran on the Catalyst app internally to test with
intersection observers end to end.
Behind the `enableSrcObject` flag. This is revisiting a variant of what
was discussed in #11163.
Instead of supporting the [`srcObject`
property](https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/srcObject)
as a separate name, this adds an overload of `src` to allow objects to
be passed. The DOM needs to add separate properties for the object forms
since you read back but it doesn't make sense for React's write-only API
to do that. Similar to how we'll like add an overload for
`popoverTarget` instead of calling it `popoverTargetElement` and how
`style` accepts an object and it's not `styleObject={{...}}`.
There are a number of reason to revisit this.
- It's just way more convenient to have this built-in and it makes
conceptual sense. We typically support declarative APIs and polyfill
them when necessary.
- RSC supports Blobs and by having it built-in you don't need a Client
Component wrapper to render it where as doing it with effects would
require more complex wrappers. By picking Blobs over base64,
client-navigations can use the more optimized binary encoding in the RSC
protocol.
- The timing aspect of coordinating it with Suspensey images and image
decoding is a bit tricky to get right because if you set it in an effect
it's too late because you've already rendered it.
- SSR gets complicated when done in user space because you have to
handle both branches. Likely with `useSyncExternalStore`.
- By having it built-in we could optimize the payloads shared between
RSC payloads embedded in the HTML and data URLs.
This does not support objects for `<source src>` nor `<img srcset>`.
Those don't really have equivalents in the DOM neither. They're mainly
for picking an option when you don't know programmatically. However, for
this use case you're really better off picking a variant before
generating the blobs.
We may support Response objects in the future too as per
https://github.com/whatwg/fetch/issues/49
We've known we've wanted this for many years and most of the
implementation was already done for Suspensey CSS. This waits to commit
until images have decoded by default or up to 500ms timeout (same as
suspensey fonts).
It only applies to Transitions, Retries (Suspense), Gesture Transitions
(flag) and Idle (doesn't exist). Sync updates just commit immediately.
`<img loading="lazy" src="..." />` opts out since you explicitly want it
to load lazily in that case.
`<img onLoad={...} src="..." />` also opts out since that implies you're
ok with managing your own reveal.
In the future, we may add an opt in e.g. `<img blocking="render"
src="..." />` that opts into longer timeouts and re-suspends even sync
updates. Perhaps also triggering error boundaries on errors.
The rollout for this would have to go in a major and we may have to
relax the default timeout to not delay too much by default. However, we
can also make this part of `enableViewTransition` so that if you opt-in
by using View Transitions then those animations will suspend on images.
That we could ship in a minor.
Stacked on #32785.
This is now replaced by `startGestureTransition` added in #32785.
I also renamed the flag from `enableSwipeTransition` to
`enableGestureTransition` to correspond to the new name.
https://github.com/facebook/react/pull/32529 added a dynamic flag for
this, but that breaks tests since the flags are not defined everywhere.
However, this is a static value and the flag is only for supporting
existing tests. So we can override it in the test config, and make it
static at built time instead.
*This API is experimental and subject to change or removal.*
This PR is an alternative to
https://github.com/facebook/react/pull/32421 based on feedback:
https://github.com/facebook/react/pull/32421#pullrequestreview-2625382015
. The difference here is that we traverse from the Fragment's fiber at
operation time instead of keeping a set of children on the
`FragmentInstance`. We still need to handle newly added or removed child
nodes to apply event listeners and observers, so we treat those updates
as effects.
**Fragment Refs**
This PR extends React's Fragment component to accept a `ref` prop. The
Fragment's ref will attach to a custom host instance, which will provide
an Element-like API for working with the Fragment's host parent and host
children.
Here I've implemented `addEventListener`, `removeEventListener`, and
`focus` to get started but we'll be iterating on this by adding
additional APIs in future PRs. This sets up the mechanism to attach refs
and perform operations on children. The FragmentInstance is implemented
in `react-dom` here but is planned for Fabric as well.
The API works by targeting the first level of host children and proxying
Element-like APIs to allow developers to manage groups of elements or
elements that cannot be easily accessed such as from a third-party
library or deep in a tree of Functional Component wrappers.
```javascript
import {Fragment, useRef} from 'react';
const fragmentRef = useRef(null);
<Fragment ref={fragmentRef}>
<div id="A" />
<Wrapper>
<div id="B">
<div id="C" />
</div>
</Wrapper>
<div id="D" />
</Fragment>
```
In this case, calling `fragmentRef.current.addEventListener()` would
apply an event listener to `A`, `B`, and `D`. `C` is skipped because it
is nested under the first level of Host Component. If another Host
Component was appended as a sibling to `A`, `B`, or `D`, the event
listener would be applied to that element as well and any other APIs
would also affect the newly added child.
This is an implementation of the basic feature as a starting point for
feedback and further iteration.
