I was experimenting with animations in SuspenseList and hit a crash
using ViewTransition as a direct child with `revealOrder="together"`
```
TypeError: Cannot read properties of null (reading 'autoName')
33 | return props.name;
34 | }
> 35 | if (instance.autoName !== null) {
| ^
36 | return instance.autoName;
37 | }
```
When ViewTransition is direct child of SuspenseList, the second render
pass calls resetChildFibers, setting stateNode to null. Other fibers
create stateNode in completeWork. ViewTransition does not, so stateNode
is lost.
Followed the pattern used for Offscreen to update stateNode in beginWork
if it is null.
Also added a regression test.
Stacked on #35487.
This is slightly different because the first suspended commit is on
blockers that prevent us from committing which still needs to be
resolved first.
If a gesture lane has to be rerendered while the gesture is happening
then it reenters this state with a new tree. (Currently this doesn't
happen for a ping I think which is not really how it usually works but
better in this case.)
If an initial value is specified, then it's always used regardless as
part of the gesture render.
If a gesture render causes an update, then previously that was not
treated as deferred and could therefore be blocking the render. However,
a gesture is supposed to flush synchronously ideally. Therefore we
should consider these as urgent.
The effect is that useDeferredValue renders the previous state.
Stacked on #35486.
When a Gesture commits, it leaves behind work on a Transition lane
(`revertLane`). This entangles that lane with whatever lane we're using
in the event that cancels the Gesture. This ensures that the revert and
the result of any resulting Action commits as one batch. Typically the
Action would apply a new state that is similar or the same as the revert
of the Gesture.
This makes it resilient to unbatching in #35392.
Stacked on #35485.
Before this PR, the `startGestureTransition` API would itself never
commit its state. After the gesture releases it stops the animation in
the next commit which just leaves the DOM tree in the original state. If
there's an actual state change from the Action then that's committed as
the new DOM tree. To avoid animating from the original state to the new
state again, this is DOM without an animation. However, this means that
you can't have the actual action committing be in a slightly different
state and animate between the final gesture state and into the new
action.
Instead, we now actually keep the render tree around and commit it in
the end. Basically we assume that if the Timeline was closer to the end
then visually you're already there and we can commit into that state.
Most of the time this will be at the actual end state when you release
but if you have something else cancelling the gesture (e.g.
`touchcancel`) it can still commit this state even though your gesture
recognizer might not consider this an Action. I think this is ok and
keeps it simple.
When the gesture lane commits, it'll leave a Transition behind as work
from the revert lanes on the Optimistic updates. This means that if you
don't do anything in the Action this will cause another commit right
after which reverts. This revert can animate the snap back.
There's a few fixes needed in follow up PRs:
- Fixed in #35487. ~To support unentangled Transitions we need to
explicitly entangle the revert lane with the Action to avoid committing
a revert followed by a forward instead of committing the forward
entangled with the revert. This just works now since everything is
entangled but won't work with #35392.~
- Fixed in #35510. ~This currently rerenders the gesture lane once
before committing if it was already completed but blocked. We should be
able to commit the already completed tree as is.~
When Fiber replays work after suspending and resolving in a microtask it
stripped the Forked flag from Fibers because this flag type was not
considered a Static flag. The Forked nature of a Fiber is not render
dependent and should persist after unwinding work. By making this change
the replay correctly generates the necessary tree context.
When a View Transition might not need to update we add it to a queue. If
the parent are able to be reverted, we then cancel the already started
view transitions. We do this by adding an animation that hides the "old"
state and remove the view transition name from the old state.
There was a bug where if you have more than one child in a
`<ViewTransition>` we didn't add the right suffix to the name we added
in the queue so it wasn't adding an animation that hides the old state.
The effect was that it playing an exit animation instead of being
cancelled.
Requires full error message in assert helpers.
Some of the error messages we asset on add a native javascript stack
trace, which would be a pain to add to the messages and maintain. This
PR allows you to just add `\n in <stack>` placeholder to the error
message to denote a native stack trace is present in the message.
---
Note: i vibe coded this so it was a pain to backtrack this to break this
into a stack, I tried and gave up, sorry.
When hydrating if something suspends and then resolves in a microtask it
is possible that React will resume the render without fully unwinding
work in progress. This can cause hydration cursors to be offset and lead
to hydration errors. This change adds a restore step when replaying
HostComponent to ensure the hydration cursor is in the appropriate
position when replaying.
fixes: #35210
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.
This PR updates the behavior of Activity so that when it is hidden, it
hides the contents of any portals contained within it.
Previously we had intentionally chosen not to implement this behavior,
because it was thought that this concern should be left to the userspace
code that manages the portal, e.g. by adding or removing the portal
container from the DOM. Depending on the use case for the portal, this
is often desirable anyway because the portal container itself is not
controlled by React.
However, React does own the _contents_ of the portal, and we can hide
those elements regardless of what the user chooses to do with the
container. This makes the hiding/unhiding behavior of portals with
Activity automatic in the majority of cases, and also benefits from
aligning the DOM mutations with the rest of the React's commit phase
lifecycle.
The reason we have to special case this at all is because usually we
only hide the direct DOM children of the Activity boundary. There's no
reason to go deeper than that, because hiding a parent DOM element
effectively hides everything inside of it. Portals are the exception,
because they don't exist in the normal DOM hierarchy; we can't assume
that just because a portal has a parent in the React tree that it will
also have that parent in the actual DOM.
So, whenever an Activity boundary is hidden, we must search for and hide
_any_ portal that is contained within it, and recursively hide its
direct children, too.
To optimize this search, we use a new subtree flag, PortalStatic, that
is set only on fiber paths that contain a HostPortal. This lets us skip
over any subtree that does not contain a portal.
If an error is thrown inside a hidden Activity, it should not escape
into the visible part of the UI. Conceptually, a hidden Activity
boundary is not part of the current UI; it's the same as an unmounted
tree, except for the fact that the state will be restored if it's later
revealed.
Fixes:
- https://github.com/facebook/react/issues/35073
Also, don't not skip hidden trees.
Memoized state is null when an Offscreen boundary (Suspense or Activity)
is visible.
This logic was inversed in a couple of View Transition checks which
caused pairs to be discovered or not discovered incorrectly for
insertion and deletion of Suspense or Activity boundaries.
Follow up to #35022.
It's now replaced by the `defer` option.
Sounds like nobody is actually using this option, including Meta, so we
can just delete it.
We've long had the CPU suspense feature behind a flag under the terrible
API `unstable_expectedLoadTime={arbitraryNumber}`. We've known for a
long time we want it to just be `defer={true}` (or just `<Suspense
defer>` in the short hand syntax). So this adds the new name and warns
for the old name.
For only the new name, I also implemented SSR semantics in Fizz. It has
two effects here.
1) It renders the fallback before the content (similar to prerender)
allowing siblings to complete quicker.
2) It always outlines the result. When streaming this should really
happen naturally but if you defer a prerendered content it also implies
that it's expensive and should be outlined. It gives you a opt-in to
outlining similar to suspensey images and css but let you control it
manually.
Normally if you suspend in a SuspenseList row above a Suspense boundary
in that row, it'll suspend the parent. Which can itself delay the commit
or resuspend a parent boundary. That's because SuspenseList mostly just
coordinates the state of the inner boundaries and isn't a boundary
itself.
However, for tail "hidden" and "collapsed" this is not quite the case
because the rows themselves can avoid being rendered.
In the case of "collapsed" we require at least one Suspense boundary
above to have successfully rendered before committing the list because
the idea of this mode is that you should at least always show some
indicator that things are still loading. Since we'd never try the next
one after that at all, this just works. Expect there was an unrelated
bug that meant that "suspend with delay" on a Retry didn't suspend the
commit. This caused a scenario were it'd allow a commit proceed when it
shouldn't. So I fixed that too. The counter intuitive thing here is that
we won't actually show a previous completed row if the loading state of
the next row is still loading.
For tail "hidden" it's a little different because we don't actually
require any loading indicator at all to be shown while it's loading. If
we attempt a row and it suspends, we can just hide it (and the rest) and
move to commit. Therefore this implements a path where if all the rest
of the tail are new mounts (we wouldn't be required to unmount any
existing boundaries) then we can treat the SuspenseList boundary itself
as "catching" the suspense. This is more coherent semantics since any
future row that we didn't attempt also wouldn't resuspend the parent.
This allows simple cases like `<SuspenseList>{list}</SuspenseList>` to
stream in each row without any indicator and no need for Suspense
boundaries.
Stacked on #35018.
This mounts the children of SuspenseList backwards. Meaning the first
child is mounted last in the DOM (and effect list). It's like calling
reverse() on the children.
This is meant to set us up for allowing AsyncIterable children where the
unknown number of children streams in at the end (which is the beginning
in a backwards SuspenseList). For consistency we do that with other
children too.
`unstable_legacy-backwards` still exists for the old mode but is meant
to be deprecated.
<img width="100" alt="image"
src="https://github.com/user-attachments/assets/5c2a95d7-34c4-4a4e-b602-3646a834d779"
/>
We have warned about this for a while now so we can make the switch.
Often when you reach for SuspenseList, you mean forwards. It doesn't
make sense to have the default to just be a noop. While "together" is
another useful mode that's more like a Group so isn't so associated with
the default as List. So we're switching it.
However, tail=hidden isn't as obvious of a default it does allow for a
convenient pattern for streaming in list of items by default.
This doesn't yet switch the rendering order of "backwards". That's
coming in a follow up.
Now that RN is only on the New Architecture, we can stop stop syncing
the legacy React Native renderers.
In this diff, I just stop syncing them. In a follow up I'll delete the
code for them so only Fabric is left.
This will also allow us to remove the `enableLegacyMode` feature flag.
Fixes https://github.com/facebook/react/issues/34770.
We need to clear measures at some point, otherwise all these copies of
props that we end up recording will allocate too much memory in
Chromium. This adds `performance.clearMeasures(...)` calls to such cases
in DEV.
Validated that entries are still shown on Performance panel timeline.
If an inner Offscreen commits an unhide, but an outer Offscreen is still
hidden but they're controlling the same DOM node then we shouldn't
unhide the DOM node yet.
This keeps track of whether we're directly inside a hidden offscreen. It
might be better to just do the tree search instead of keeping the stack
state since it's a rare case. Although this hide/unhide path does
trigger a lot of times even when there's no change.
This was technically a bug with Suspense too but it doesn't appear
because a suspended Suspense boundary never commits its partial state.
If it did, it would trigger this same path. But it can happen with an
outer Activity and inner Suspense.
## Overview
This PR ships the View Transition APIs to `react@canary`:
- [`<ViewTransition
/>`](https://react.dev/reference/react/ViewTransition)
-
[`addTransitionType`](https://react.dev/reference/react/addTransitionType)
This means these APIs are ready for final feedback and prepare for
semver stable release.
## What this means
Shipping `<ViewTransition />` and `addTransitionType` to canary means
they have gone through extensive testing in production, we are confident
in the stability of the APIs, and we are preparing to release it in a
future semver stable version.
Libraries and frameworks following the [Canary
Workflow](https://react.dev/blog/2023/05/03/react-canaries) should begin
implementing and testing these features.
## Why we follow the Canary Workflow
To prepare for semver stable, libraries should test canary features like
`<ViewTransition />` with `react@canary` to confirm compatibility and
prepare for the next semver release in a myriad of environments and
configurations used throughout the React ecosystem. This provides
libraries with ample time to catch any issues we missed before slamming
them with problems in the wider semver release.
Since these features have already gone through extensive production
testing, and we are confident they are stable, frameworks following the
[Canary Workflow](https://react.dev/blog/2023/05/03/react-canaries) can
also begin adopting canary features like `<ViewTransition />`.
This adoption is similar to how different Browsers implement new
proposed browser features before they are added to the standard. If a
frameworks adopts a canary feature, they are committing to stability for
their users by ensuring any API changes before a semver stable release
are opaque and non-breaking to their users.
Apps not using a framework are also free to adopt canary features like
`<ViewTransition>` as long as they follow the [Canary
Workflow](https://react.dev/blog/2023/05/03/react-canaries), but we
generally recommend waiting for a semver stable release unless you have
the capacity to commit to following along with the canary changes and
debugging library compatibility issues.
Waiting for semver stable means you're able to benefit from libraries
testing and confirming support, and use semver as signal for which
version of a library you can use with support of the feature.
## Docs
Check out the ["React Labs: View Transitions, Activity, and
more"](https://react.dev/blog/2025/04/23/react-labs-view-transitions-activity-and-more#view-transitions)
blog post, and [the new docs for `<ViewTransition
/>`](https://react.dev/reference/react/ViewTransition) and
[`addTransitionType`](https://react.dev/reference/react/addTransitionType)
for more info.
Reset EventTime when clearing timers. We need to track repeat updates
separately.
Typically we always reset all timers when we've logged an update. The
same update shouldn't be logged again.
I was trying to be clever and not reset the XEventTime because we also
need the timestamp to know if it's a repeat event. However, because of
this it looked like we had an event schedule an update even after we had
reset them.
This always resets the XEventTime to -1.1 and then stashes the old time
on EventRepeatTime which is our indication whether the next update was a
repeat of the old event.
---------
Co-authored-by: Ruslan Lesiutin <28902667+hoxyq@users.noreply.github.com>
Co-authored-by: Ricky <rickhanlonii@gmail.com>
We've observed some scenarios, where cascading update happens in an
effect that was shorter than 0.05ms. In this case, this effect won't be
displayed on a timeline, because of the threshold that we are using, but
it would be shown in entry properties or in a stack trace.
To avoid confusion, we should always log such effects.
Validated via manually changing the threshold to 100ms+ and observing
that only effects that triggered an update are visible on a timeline.
Otherwise, when a context is propagated into an Activity (or Suspense)
this will leave work behind on the Offscreen component itself. Which
will cause an extra unnecessary render and commit pass just to figure
out that we're still defering it to idle.
This is because lazy context propagation, when calling to schedule some
work walks back up the tree all the way to the root. This is usually
fine for other nodes since they'll recompute their remaining child lanes
on the way up. However, for the Offscreen component we'll have already
computed it. We need to set it after propagation to ensure it gets
reset.
## 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
When forcing suspense/error we're doing that by scheduling a sync update
on the fiber. Resuspending a Suspense boundary can only happen sync
update so that makes sense. Erroring also forces a sync commit. This
means that no View Transitions fire.
However, unsuspending (and dismissing an error dialog) can be async so
the reveal should be able to be async.
This adds another hook for scheduling using the Retry lane. That way
when you play through a reveal sequence of Suspense boundaries (like
playing through the timeline), it'll run the animations that would've
ran during a loading sequence.
Bumps `useEffectEvent` from `@experimental` to `@canary`. Removes the
`experimental_` prefix from the export.
## TODO
- [ ] Update useEffectEvent reference page and Canary badging in docs:
https://github.com/reactjs/react.dev/pull/8025
Stacked on #34546.
Same as #34538 but for gestures.
Includes various fixes.
This shows how it ends with a Transition when you release in the
committed state. Note how the Animation of the Gesture continues until
the Transition is done so that the handoff is seamless.
<img width="853" height="134" alt="Screenshot 2025-09-20 at 7 37 29 PM"
src="https://github.com/user-attachments/assets/6192a033-4bec-43b9-884b-77e3a6f00da6"
/>
This helper weirdly doesn't include the sync lane.
Everywhere we use it we have to check the sync lane separately. We can
simplify things by simply including the sync lane.
This fixes a lack of optimization because we should not check the store
consistency for a `flushSync` render.
d91d28c8ba/packages/react-reconciler/src/ReactFiberHooks.js (L1691-L1693)
Stacked on #34538.
Track the Task of the first ViewTransition that we detected as
animating. Use this as the Task as "Starting Animation", "Animating"
etc. That way you can see which ViewTransition spawned the Animation.
Although it's likely to be multiple.
<img width="757" height="393" alt="Screenshot 2025-09-19 at 10 19 18 PM"
src="https://github.com/user-attachments/assets/a6cdcb89-bd02-40ec-b3c3-11121c29e892"
/>
Stacked on #34522.
<img width="1025" height="200" alt="Screenshot 2025-09-19 at 6 37 28 PM"
src="https://github.com/user-attachments/assets/f25900f6-6503-48b1-876d-bd6697a29c6f"
/>
We already cover the time between "Starting Animation" and "Remaining
Effects" as "Animating". However, if the effects are forced then we can
still be animating after that. This fills in that gap.
This also fills in the gap if another render starts before the animation
finishes on the same track. It'll mark the blank space between the
previous render finishing and the next render starting as "Animating".
This should correspond roughly to the native "Animations" track.
