This adds a regression test and fix for a case where a sync update
triggers selective hydration, which then leads to a "Maximum update
depth exceeded" error, even though there was only a single update. This
happens when a single sync update flows into many sibling dehydrated
Suspense boundaries.
This fix is, if a commit was the result of selective hydration, we
should not increment the nested update count, because those renders
conceptually are not updates.
Ideally, they wouldn't even be in a separate commit — we should be able
to hydrate a tree and apply an update on top of it within the same
render phase. We could do this once we implement resumable context
stacks.
`performSyncWorkOnRoot` has only a single caller, and the caller already
computes the next lanes (`getNextLanes`) before deciding to call the
function. So we can pass them as an argument instead of computing the
lanes again.
There was already a TODO comment about this, but it was mostly perf
related. However, @rickhanlonii noticed a discrepancy where the inner
`getNextLanes` call was not being passed the current work-in- progress
lanes. Usually this shouldn't matter because there should never be
work-in-progress sync work; it should finish immediately. There is one
case I'm aware of where we exit the work loop without finishing a sync
render, which is selective hydration, but even then it should switch to
the sync hydration lane, not the normal sync lane. So something else is
probably going on. I suspect it might be related to the
`enableUnifiedSyncLane` experiment.
This is likely related to a regression found internally at Meta. We're
still working on getting a proper regression test; I can come up with a
contrived one but I'm not confident it'll be the same as the actual
regression until we get a better repro.
This is an optimization where useFormState will only emit extra comment
markers if a form state is passed at the root. If no state is passed, we
don't need to emit anything because none of the hooks will match.
During an MPA form submission, useFormState should only reuse the form
state if same action is passed both times. (We also compare the key
paths.)
We compare the identity of the inner closure function, disregarding the
value of the bound arguments. That way you can pass an inline Server
Action closure:
```js
function FormContainer({maxLength}) {
function submitAction(prevState, formData) {
'use server'
if (formData.get('field').length > maxLength) {
return { errorMsg: 'Too many characters' };
}
// ...
}
return <Form submitAction={submitAction} />
}
```
If a Server Action is passed to useFormState, the action may be
submitted before it has hydrated. This will trigger a full page
(MPA-style) navigation. We can transfer the form state to the next page
by comparing the key path of the hook instance.
`ReactServerDOMServer.decodeFormState` is used by the server to extract
the form state from the submitted action. This value can then be passed
as an option when rendering the new page. It must be passed during both
SSR and hydration.
```js
const boundAction = await decodeAction(formData, serverManifest);
const result = await boundAction();
const formState = decodeFormState(result, formData, serverManifest);
// SSR
const response = createFromReadableStream(<App />);
const ssrStream = await renderToReadableStream(response, { formState })
// Hydration
hydrateRoot(container, <App />, { formState });
```
If the `formState` option is omitted, then the state won't be
transferred to the next page. However, it must be passed in both places,
or in neither; misconfiguring will result in a hydration mismatch.
(The `formState` option is currently prefixed with `experimental_`)
A planned feature of useFormState is that if the page load is the result
of an MPA-style form submission — i.e. a form was submitted before it
was hydrated, using Server Actions — the state of the hook should
transfer to the next page.
I haven't implemented that part yet, but as a prerequisite, we need some
way for Fizz to indicate whether a useFormState hook was rendered using
the "postback" state. That way we can do all state matching logic on the
server without having to replicate it on the client, too.
The approach here is to emit a comment node for each useFormState hook.
We use one of two comment types: `<!--F-->` for a normal useFormState
hook, and `<!--F!-->` for a hook that was rendered using the postback
state. React will read these markers during hydration. This is similar
to how we encode Suspense boundaries.
Again, the actual matching algorithm is not yet implemented — for now,
the "not matching" marker is always emitted.
We can optimize this further by not emitting any markers for a render
that is not the result of a form postback, which I'll do in subsequent
PRs.
When the `permalink` option is passed to `useFormState`, and the form is
submitted before it has hydrated, the permalink will be used as the
target of the form action, enabling MPA-style form submissions.
(Note that submitting a form without hydration is a feature of Server
Actions; it doesn't work with regular client actions.)
It does not have any effect after the form has hydrated.
## Summary
Fixes: https://github.com/facebook/react/issues/27296
On actions that cause a component to change its signature, and therefore
to remount, the `_debugSource` property of the fiber updates in delay
and causes the `devtools` source field to vanish.
This issue happens in
https://github.com/facebook/react/blob/main/packages/react-reconciler/src/ReactFiberBeginWork.js
```js
function beginWork(
current: Fiber | null,
workInProgress: Fiber,
renderLanes: Lanes,
): Fiber | null {
if (__DEV__) {
if (workInProgress._debugNeedsRemount && current !== null) {
// This will restart the begin phase with a new fiber.
return remountFiber(
current,
workInProgress,
createFiberFromTypeAndProps(
workInProgress.type,
workInProgress.key,
workInProgress.pendingProps,
workInProgress._debugOwner || null,
workInProgress.mode,
workInProgress.lanes,
),
);
}
}
// ...
```
`remountFiber` uses the 3rd parameter as the new fiber
(`createFiberFromTypeAndProps(...)`), but this parameter doesn’t contain
a `_debugSource`.
## How did you test this change?
Tested by monkey patching
`./node_modules/react-dom/cjs/react-dom.development.js`:
<img width="1749" alt="image"
src="https://github.com/facebook/react/assets/75563024/ccaf7fab-4cc9-4c05-a48b-64db6f55dc23">
https://github.com/facebook/react/assets/75563024/0650ae5c-b277-44d1-acbb-a08d98bd38e0
This implements useFormState in Fiber. (It does not include any
progressive enhancement features; those will be added later.)
useFormState is a hook for tracking state produced by async actions. It
has a signature similar to useReducer, but instead of a reducer, it
accepts an async action function.
```js
async function action(prevState, payload) {
// ..
}
const [state, dispatch] = useFormState(action, initialState)
```
Calling dispatch runs the async action and updates the state to the
returned value.
Async actions run before React's render cycle, so unlike reducers, they
can contain arbitrary side effects.
A transition that flows into a dehydrated boundary should not suspend if
the boundary is showing a fallback.
This is related to another issue where Fizz streams in the initial HTML
after a client navigation has already happened. That issue is not fixed
by this commit, but it does make it less likely. Need to think more
about the larger issue.
This exposes, but does not yet implement, a new experimental API called
useFormState. It's gated behind the enableAsyncActions flag.
useFormState has a similar signature to useReducer, except instead of a
reducer it accepts an (async) action function. React will wait until the
promise resolves before updating the state:
```js
async function action(prevState, payload) {
// ..
}
const [state, dispatch] = useFormState(action, initialState)
```
When used in combination with Server Actions, it will also support
progressive enhancement — a form that is submitted before it has
hydrated will have its state transferred to the next page. However, like
the other action-related hooks, it works with fully client-driven
actions, too.
This fixes the regression test added in the previous commit. The
"Suspensey commit" implementation relies on the
`shouldRemainOnPreviousScreen` function to determine whether to 1)
suspend the commit 2) activate a parent fallback and schedule a retry.
The issue was that we were sometimes attempting option 2 even when there
was no parent fallback.
Part of the reason this bug landed is due to how `throwException` is
structured. In the case of Suspensey commits, we pass a special "noop"
thenable to `throwException` as a way to trigger the Suspense path. This
special thenable must never have a listener attached to it. This is not
a great way to structure the logic, it's just a consequence of how the
code evolved over time. We should refactor it into multiple functions so
we can trigger a fallback directly without having to check the type. In
the meantime, I added an internal warning to help detect similar
mistakes in the future.
Search for more generic fork files if an exact match does not exist. If
`forks/MyFile.dom.js` exists but `forks/MyFile.dom-node.js` does not
then use it when trying to resolve forks for the `"dom-node"` renderer
in flow, tests, and build
consolidate certain fork files that were identical and make semantic
sense to be generalized
add `dom-browser-esm` bundle and use it for
`react-server-dom-esm/client.browser` build
This adds an experimental `unstable_postpone(reason)` API.
Currently we don't have a way to model effectively an Infinite Promise.
I.e. something that suspends but never resolves. The reason this is
useful is because you might have something else that unblocks it later.
E.g. by updating in place later, or by client rendering.
On the client this works to model as an Infinite Promise (in fact,
that's what this implementation does). However, in Fizz and Flight that
doesn't work because the stream needs to end at some point. We don't
have any way of knowing that we're suspended on infinite promises. It's
not enough to tag the promises because you could await those and thus
creating new promises. The only way we really have to signal this
through a series of indirections like async functions, is by throwing.
It's not 100% safe because these values can be caught but it's the best
we can do.
Effectively `postpone(reason)` behaves like a built-in [Catch
Boundary](https://github.com/facebook/react/pull/26854). It's like
`raise(Postpone, reason)` except it's built-in so it needs to be able to
be encoded and caught by Suspense boundaries.
In Flight and Fizz these behave pretty much the same as errors. Flight
just forwards it to retrigger on the client. In Fizz they just trigger
client rendering which itself might just postpone again or fill in the
value. The difference is how they get logged.
In Flight and Fizz they log to `onPostpone(reason)` instead of
`onError(error)`. This log is meant to help find deopts on the server
like finding places where you fall back to client rendering. The reason
that you pass in is for that purpose to help the reason for any deopts.
I do track the stack trace in DEV but I don't currently expose it to
`onPostpone`. This seems like a limitation. It might be better to expose
the Postpone object which is an Error object but that's more of an
implementation detail. I could also pass it as a second argument.
On the client after hydration they don't get passed to
`onRecoverableError`. There's no global `onPostpone` API to capture
postponed things on the client just like there's no `onError`. At that
point it's just assumed to be intentional. It doesn't have any `digest`
or reason passed to the client since it's not logged.
There are some hacky solutions that currently just tries to reuse as
much of the existing code as possible but should be more properly
implemented.
- Fiber is currently just converting it to a fake Promise object so that
it behaves like an infinite Promise.
- Fizz is encoding the magic digest string `"POSTPONE"` in the HTML so
we know to ignore it but it should probably just be something neater
that doesn't share namespace with digests.
Next I plan on using this in the `/static` entry points for additional
features.
Why "postpone"? It's basically a synonym to "defer" but we plan on using
"defer" for other purposes and it's overloaded anyway.
This adds a regression test for a bug where, after a store mutation, the
updated data causes the shell of the app to suspend.
When re-rendering due to a concurrent store mutation, we must check for
the RootDidNotComplete exit status again.
As a follow-up, I'm going to look into to cleaning up the places where
we check the exit status, so bugs like these are less likely. I think we
might be able to combine most of it into a single switch statement.
## Summary
Since we are enabling `useModernStrictMode` flag internally, to make
sure the internal testing of half StrictMode doesn't suddenly break,
this PR makes sure it also works with `useModernStrictMode` true.
## Test plan:
Manually set `useModernStrictMode` to true.
`yarn test ReactOffscreenStrictMode-test -r=www-modern --env=development
--variant=true`
`yarn test ReactStrictMode-test.internal -r=www-modern --env=development
--variant=true`
## Summary
as we began [discussing
yesterday](https://github.com/facebook/react/pull/27056#discussion_r1253282784),
`SuspenseList` is not actually stable yet, and should likely be exported
with the `unstable_` prefix.
the conversation yesterday began discussing this in the context of the
fb-specific packages, but changing it there without updating everywhere
else leads to test failures, so here the change is made across packages.
## How did you test this change?
```
yarn flow dom-browser
yarn test
```
Adds a development warning to complement the error introduced by
https://github.com/facebook/react/pull/27019.
We can detect and warn about async client components by checking the
prototype of the function. This won't work for environments where async
functions are transpiled, but for native async functions, it allows us
to log an earlier warning during development, including in cases that
don't trigger the infinite loop guard added in
https://github.com/facebook/react/pull/27019. It does not supersede the
infinite loop guard, though, because that mechanism also prevents the
app from crashing.
I also added a warning for calling a hook inside an async function. This
one fires even during a transition. We could add a corresponding warning
to Flight, since hooks are not allowed in async Server Components,
either. (Though in both environments, this is better handled by a lint
rule.)
Suspending with an uncached promise is not yet supported. We only
support suspending on promises that are cached between render attempts.
(We do plan to partially support this in the future, at least in certain
constrained cases, like during a route transition.)
This includes the case where a component returns an uncached promise,
which is effectively what happens if a Client Component is authored
using async/await syntax.
This is an easy mistake to make in a Server Components app, because
async/await _is_ available in Server Components.
In the current behavior, this can sometimes cause the app to crash with
an infinite loop, because React will repeatedly keep trying to render
the component, which will result in a fresh promise, which will result
in a new render attempt, and so on. We have some strategies we can use
to prevent this — during a concurrent render, we can suspend the work
loop until the promise resolves. If it's not a concurrent render, we can
show a Suspense fallback and try again at concurrent priority.
There's one case where neither of these strategies work, though: during
a sync render when there's no parent Suspense boundary. (We refer to
this as the "shell" of the app because it exists outside of any loading
UI.)
Since we don't have any great options for this scenario, we should at
least error gracefully instead of crashing the app.
So this commit adds a detection mechanism for render loops caused by
async client components. The way it works is, if an app suspends
repeatedly in the shell during a synchronous render, without committing
anything in between, we will count the number of attempts and eventually
trigger an error once the count exceeds a threshold.
In the future, we will consider ways to make this case a warning instead
of a hard error.
See https://github.com/facebook/react/issues/26801 for more details.
This PR contains a regression test and two separate fixes: a targeted
fix, and a more general one that's designed as a last-resort guard
against these types of bugs (both bugs in app code and bugs in React).
I confirmed that each of these fixes separately are sufficient to fix
the regression test I added.
We can't realistically detect all infinite update loop scenarios because
they could be async; even a single microtask can foil our attempts to
detect a cycle. But this improves our strategy for detecting the most
common kind.
See commit messages for more details.
## Summary
This PR cleans up `useMutableSource`. This has been blocked by a
remaining dependency internally at Meta, but that has now been deleted.
<!--
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-->
## How did you test this change?
```
yarn flow
yarn lint
yarn test --prod
```
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In https://github.com/facebook/react/pull/26914 I added an extra logic
to turn off double useEffect if there is an `Offscreen`
tag. But `Suspense` uses `Offscreen` tag internally and that turns off
`disableStrictPassiveEffect` for everything.
<!--
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4. Ensure the test suite passes (`yarn test`). Tip: `yarn test --watch
TestName` is helpful in development.
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## Summary
<!--
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does the pull request solve?
-->
We are upgrading React 17 codebase to React18, and `StrictMode` has been
great for surfacing potential production bugs on React18 for class
components. There are non-trivial number of test failures caused by
double `useEffect` in StrictMode. To prioritize surfacing and fixing
issues that will break in production now, we need a flag to turn off
double `useEffect` for now in StrictMode temporarily. This is a
Meta-only hack for rolling out `createRoot` and we will fast follow to
remove it and use full strict mode.
## How did you test this change?
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jest
When we diffInCommitPhase there's no updatePayload, which caused no
update to be applied.
This is unfortunate because it would've been a lot easier to see this
oversight if we didn't have to support both flags.
I also carified that updateHostComponent is unnecessary in the new flag.
We reuse updateHostComponent for HostSingleton and HostHoistables since
it has a somewhat complex path but that means you have to remember when
editing updateHostComponent that it's not just used for that tag.
Luckily with the new flag, this is actually unnecessary since we just
need to mark it for update if any props have changed and then we diff it
later.
This isn't really meant to be actually used, there are many issues with
this approach, but it shows the capabilities as a proof-of-concept.
It's a new reference implementation package `react-server-dom-esm` as
well as a fixture in `fixtures/flight-esm` (fork of `fixtures/flight`).
This works pretty much the same as pieces we already have in the Webpack
implementation but instead of loading modules using Webpack on the
client it uses native browser ESM.
To really show it off, I don't use any JSX in the fixture and so it also
doesn't use Babel or any compilation of the files.
This works because we don't actually bundle the server in the reference
implementation in the first place. We instead use [Node.js
Loaders](https://nodejs.org/api/esm.html#loaders) to intercept files
that contain `"use client"` and `"use server"` and replace them. There's
a simple check for those exact bytes, and no parsing, so this is very
fast.
Since the client isn't actually bundled, there's no module map needed.
We can just send the file path to the file we want to load in the RSC
payload for client references.
Since the existing reference implementation for Node.js already used ESM
to load modules on the server, that all works the same, including Server
Actions. No bundling.
There is one case that isn't implemented here. Importing a `"use
server"` file from a Client Component. We don't have that implemented in
the Webpack reference implementation neither - only in Next.js atm. In
Webpack it would be implemented as a Webpack loader.
There are a few ways this can be implemented without a bundler:
- We can intercept the request from the browser importing this file in
the HTTP server, and do a quick scan for `"use server"` in the file and
replace it just like we do with loaders in Node.js. This is effectively
how Vite works and likely how anyone using this technique would have to
support JSX anyway.
- We can use native browser "loaders" once that's eventually available
in the same way as in Node.js.
- We can generate import maps for each file and replace it with a
pointer to a placeholder file. This requires scanning these ahead of
time which defeats the purposes.
Another case that's not implemented is the inline `"use server"` closure
in a Server Component. That would require the existing loader to be a
bit smarter but would still only "compile" files that contains those
bytes in the fast path check. This would also happen in the loader that
already exists so wouldn't do anything substantially different than what
we currently have here.
Currently we preload all scripts that are not hoisted. One of the
original reasons for this is we stopped SSR rendering async scripts that
had an onLoad/onError because we needed to be able to distinguish
between Float scripts and non-Float scripts during hydration. Hydration
has been refactored a bit and we can not get around this limitation so
we can just emit the async script in place. However, sync and defer
scripts are also preloaded. While this is sometimes desirable it is not
universally so and there are issues with conveying priority properly
(see fetchpriority) so with this change we remove the automatic
preloading of non-Float scripts altogether.
For this change to make sense we also need to emit async scripts with
loading handlers during SSR. we previously only preloaded them during
SSR because it was necessary to keep async scripts as unambiguously
resources when hydrating. One ancillary benefit was that load handlers
would always fire b/c there was no chance the script would run before
hydration. With this change we go back to having the ability to have
load handlers fired before hydration. This is already a problem with
images and we don't have a generalized solution for it however our
likely approach to this sort of thing where you need to wait for a
script to load is to use something akin to `importScripts()` rather than
rendering a script with onLoad.
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## Summary
<!--
Explain the **motivation** for making this change. What existing problem
does the pull request solve?
-->
In StrictMode, React currently only triggers `componentWillUnmount` if
`componentDidMount` is defined. This would miss detecting issues like
initializing resources in constructor or componentWillMount, for
example:
```
class Component {
constructor() {
this._subscriptions = new Subscriptions();
}
componentWillUnmount() {
this._subscriptions.reset();
}
}
```
The PR makes `componentWillUnmount` always run in StrictMode.
## How did you test this change?
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`yarn test ci`
## Overview
Does a few things:
- Renames `enableSyncDefaultUpdates` to
`forceConcurrentByDefaultForTesting`
- Changes the way it's used so it's dead-code eliminated separate from
`allowConcurrentByDefault`
- Deletes a bunch of the gated code
The gates that are deleted are unnecessary now. We were keeping them
when we originally thought we would come back to being concurrent by
default. But we've shifted and now sync-by default is the desired
behavior long term, so there's no need to keep all these forked tests
around.
I'll follow up to delete more of the forked behavior if possible.
Ideally we wouldn't need this flag even if we're still using
`allowConcurrentByDefault`.
The bindings upstream in Relay has been removed so we don't need these
builds anymore. The idea is to revisit an FB integration of Flight but
it wouldn't use the Relay specific bindings. It's a bit unclear how it
would look but likely more like the OSS version so not worth keeping
these around.
The `dom-relay` name also included the FB specific Fizz implementation
of the streaming config so I renamed that to `dom-fb`. There's no Fizz
implementation for Native yet so I just removed `native-relay`.
We created a configurable fork for how to encode the output of Flight
and the Relay implementation encoded it as JSON objects instead of
strings/streams. The new implementation would likely be more stream-like
and just encode it directly as string/binary chunks. So I removed those
indirections so that this can just be declared inline in
ReactFlightServer/Client.
Now that the throttling mechanism applies more often, we've decided to
lower this a tad to ensure it's not noticeable. The idea is it should be
just large enough to prevent jank when lots of different parts of the UI
load in rapid succession, but not large enough to make the UI feel
sluggish. There's no perfect number, it's just a heuristic.
The throttling mechanism for fallbacks should apply to both their
appearance _and_ disappearance.
This was mostly addressed by #26611. See that PR for additional context.
However, a flaw in the implementation is that we only update the the
timestamp used for throttling when the fallback initially appears. We
don't update it when the real content pops in. If lots of content in
separate Suspense trees loads around the same time, you can still get
jank.
The issue is fixed by updating the throttling timestamp whenever the
visibility of a fallback changes. Not just when it appears.
Previously, we'd call and use getSnapshot on the second render resulting
in `Warning: Text content did not match. Server: "Nay!" Client: "Yay!"`
and then `Error: Text content does not match server-rendered HTML.`.
Fixes#26095. Closes#26113. Closes#25650.
---------
Co-authored-by: eps1lon <silbermann.sebastian@gmail.com>
This allows us to emit extra ephemeral data that will only be used on
server rendered forms.
First I refactored the shouldSkip functions to now just do that work
inside the canHydrate methods. This makes the Config bindings a little
less surface area but it also helps us optimize a bit since we now can
look at the code together and find shared paths.
canHydrate returns the instance if it matches, that used to just be
there to refine the type but it can also be used to just return a
different instance later that we find. If we don't find one, we'll bail
out and error regardless so no need to skip past anything.
This adds an experimental hook tentatively called useOptimisticState.
(The actual name needs some bikeshedding.)
The headline feature is that you can use it to implement optimistic
updates. If you set some optimistic state during a transition/action,
the state will be automatically reverted once the transition completes.
Another feature is that the optimistic updates will be continually
rebased on top of the latest state.
It's easiest to explain with examples; we'll publish documentation as
the API gets closer to stabilizing. See tests for now.
Technically the use cases for this hook are broader than just optimistic
updates; you could use it implement any sort of "pending" state, such as
the ones exposed by useTransition and useFormStatus. But we expect
people will most often reach for this hook to implement the optimistic
update pattern; simpler cases are covered by those other hooks.
This fixes a bug with `use` where if you update a component that's
currently suspended, React will sometimes mistake it for a render phase
update.
This happens because we don't reset `currentlyRenderingFiber` until the
suspended is unwound. And with `use`, that can happen asynchronously,
most commonly when the work loop is suspended during a transition.
The fix is to make sure `currentlyRenderingFiber` is only set when we're
in the middle of rendering, which used to be true until `use` was
introduced.
More specifically this means clearing `currentlyRenderingFiber` when
something throws and setting it again when we resume work.
In many cases, this bug will fail "gracefully" because the update is
still added to the queue; it's not dropped completely. It's also
somewhat rare because it has to be the exact same component that's
currently suspended. But it's still a bug. I wrote a regression test
that shows a sync update failing to interrupt a suspended component.
This hook reads the status of its ancestor form component, if it exists.
```js
const {pending, data, action, method} = useFormStatus();
```
It can be used to implement a loading indicator, for example. You can
think of it as a shortcut for implementing a loading state with the
useTransition hook.
For now, it's only available in the experimental channel. We'll share
docs once its closer to being stable. There are additional APIs that
will ship alongside it.
Internally it's implemented using startTransition + a context object.
That's a good way to think about its behavior, but the actual
implementation details may change in the future.
Because form elements cannot be nested, the implementation in the
reconciler does not bother to keep track of multiple nested "transition
providers". So although it's implemented using generic Fiber config
methods, it does currently make some assumptions based on React DOM's
requirements.
When there are multiple async actions at the same time, we entangle them
together because we can't be sure which action an update might be
associated with. (For this, we'd need AsyncContext.) However, if one of
the async actions fails with an error, it should only affect that
action, not all the other actions it may be entangled with.
Resolving each action independently also means they can have independent
pending state types, rather than being limited to an `isPending`
boolean. We'll use this to implement an upcoming form API.
This is the next step toward full support for async form actions.
Errors thrown inside form actions should cause the form to re-render and
throw the error so it can be captured by an error boundary. The behavior
is the same if the `<form />` had an internal useTransition hook, which
is pretty much exactly how we implement it, too.
The first time an action is called, the form's HostComponent is
"upgraded" to become stateful, by lazily mounting a list of hooks. The
rest of the implementation for function components can be shared.
Because the error handling behavior added in this commit is just using
useTransition under-the-hood, it also handles pending states, too.
However, this pending state can't be observed until we add a new hook
for that purpose. I'll add this next.
Stacked on #26570
Previously we restricted Float methods to only being callable while
rendering. This allowed us to make associations between calls and their
position in the DOM tree, for instance hoisting preinitialized styles
into a ShadowRoot or an iframe Document.
When considering how we are going to support Flight support in Float
however it became clear that this restriction would lead to compromises
on the implementation because the Flight client does not execute within
the context of a client render. We want to be able to disaptch Float
directives coming from Flight as soon as possible and this requires
being able to call them outside of render.
this patch modifies Float so that its methods are callable anywhere. The
main consequence of this change is Float will always use the Document
the renderer script is running within as the HoistableRoot. This means
if you preinit as style inside a component render targeting a ShadowRoot
the style will load in the ownerDocument not the ShadowRoot. Practially
speaking it means that preinit is not useful inside ShadowRoots and
iframes.
This tradeoff was deemed acceptable because these methods are
optimistic, not critical. Additionally, the other methods, preconntect,
prefetchDNS, and preload, are not impacted because they already operated
at the level of the ownerDocument and really only interface with the
Network cache layer.
I added a couple additional fixes that were necessary for getting tests
to pass that are worth considering separately.
The first commit improves the diff for `waitForThrow` so it compares
strings if possible.
The second commit makes invokeGuardedCallback not use metaprogramming
pattern and swallows any novel errors produced from trying to run the
guarded callback. Swallowing may not be the best we can do but it at
least protects React against rapid failure when something causes the
dispatchEvent to throw.
This puts the change introduced by #26611 behind a flag until Meta is
able to roll it out. Disabling the flag reverts back to the old
behavior, where retries are throttled if there's still data remaining in
the tree, but not if all the data has finished loading.
The new behavior is still enabled in the public builds.
- substr is Annex B
- substring silently flips its arguments if they're in the "wrong order", which is confusing
- slice is better than sliced bread (no pun intended) and also it works the same way on Arrays so there's less to remember
---
> I'd be down to just lint and enforce a single form just for the potential compression savings by using a repeated string.
_Originally posted by @sebmarkbage in https://github.com/facebook/react/pull/26663#discussion_r1170455401_
Implements initial (client-only) support for async actions behind a
flag. This is an experimental feature and the design isn't completely
finalized but we're getting closer. It will be layered alongside other
features we're working on, so it may not feel complete when considered
in isolation.
The basic description is you can pass an async function to
`startTransition` and all the transition updates that are scheduled
inside that async function will be grouped together. The `isPending`
flag will be set to true immediately, and only set back to false once
the async action has completed (as well as all the updates that it
triggers).
The ideal behavior would be that all updates spawned by the async action
are automatically inferred and grouped together; however, doing this
properly requires the upcoming (stage 2) Async Context API, which is not
yet implemented by browsers. In the meantime, we will fake this by
grouping together all transition updates that occur until the async
function has terminated. This can lead to overgrouping between unrelated
actions, which is not wrong per se, just not ideal.
If the `useTransition` hook is removed from the UI before an async
action has completed — for example, if the user navigates to a new page
— subsequent transitions will no longer be grouped with together with
that action.
Another consequence of the lack of Async Context is that if you call
`setState` inside an action but after an `await`, it must be wrapped in
`startTransition` in order to be grouped properly. If we didn't require
this, then there would be no way to distinguish action updates from
urgent updates caused by user input, too. This is an unfortunate footgun
but we can likely detect the most common mistakes using a lint rule.
Once Async Context lands in browsers, we can start warning in dev if we
detect an update that hasn't been wrapped in `startTransition`. Then,
longer term, once the feature is ubiquitous, we can rely on it for real
and allow you to call `setState` without the additional wrapper.
Things that are _not_ yet implemented in this PR, but will be added as
follow ups:
- Support for non-hook form of `startTransition`
- Canceling the async action scope if the `useTransition` hook is
deleted from the UI
- Anything related to server actions
Andrew Clark
Sophie Alpert
idango10
Jan Kassens
Josh Story
Sebastian Markbåge
Tianyu Yao
Noah Lemen
Ricky
