When React receives new input (via `setState`, a Suspense promise
resolution, and so on), it needs to ensure there's a rendering task
associated with the update. Most of this happens
`ensureRootIsScheduled`.
If a single event contains multiple updates, we end up running the
scheduling code once per update. But this is wasteful because we really
only need to run it once, at the end of the event (or in the case of
flushSync, at the end of the scope function's execution).
So this PR moves the scheduling logic to happen in a microtask instead.
In some cases, we will force it run earlier than that, like for
`flushSync`, but since updates are batched by default, it will almost
always happen in the microtask. Even for discrete updates.
In production, this should have no observable behavior difference. In a
testing environment that uses `act`, this should also not have a
behavior difference because React will push these tasks to an internal
`act` queue.
However, tests that do not use `act` and do not simulate an actual
production environment (like an e2e test) may be affected. For example,
before this change, if a test were to call `setState` outside of `act`
and then immediately call `jest.runAllTimers()`, the update would be
synchronously applied. After this change, that will no longer work
because the rendering task (a timer, in this case) isn't scheduled until
after the microtask queue has run.
I don't expect this to be an issue in practice because most people do
not write their tests this way. They either use `act`, or they write
e2e-style tests.
The biggest exception has been... our own internal test suite. Until
recently, many of our tests were written in a way that accidentally
relied on the updates being scheduled synchronously. Over the past few
weeks, @tyao1 and I have gradually converted the test suite to use a new
set of testing helpers that are resilient to this implementation detail.
(There are also some old Relay tests that were written in the style of
React's internal test suite. Those will need to be fixed, too.)
The larger motivation behind this change, aside from a minor performance
improvement, is we intend to use this new microtask to perform
additional logic that doesn't yet exist. Like inferring the priority of
a custom event.
The old version of prettier we were using didn't support the Flow syntax
to access properties in a type using `SomeType['prop']`. This updates
`prettier` and `rollup-plugin-prettier` to the latest versions.
I added the prettier config `arrowParens: "avoid"` to reduce the diff
size as the default has changed in Prettier 2.0. The largest amount of
changes comes from function expressions now having a space. This doesn't
have an option to preserve the old behavior, so we have to update this.
* Facebook -> Meta in copyright
rg --files | xargs sed -i 's#Copyright (c) Facebook, Inc. and its affiliates.#Copyright (c) Meta Platforms, Inc. and affiliates.#g'
* Manual tweaks
We need the regression config moduleNameMapper to come before the current moduleNameMapper so when it tries to map "/^react-dom\/([^/]+)$/ it doesn't get confused. The reason is because order in which the mappings are defined matters. Patterns are checked one by one until one fits, and the most specific rule should be listed first.
This PR adds the reactVersion pragma to tests.
Tests without the reactVersion pragma won't be run if the reactVersion pragma isn't specified.
Tested each React version manually with the pragma to make sure the tests pass
The Profiler has an advanced feature that shows why a component re-rendered. In the case of props and (class) state, it shows the names of props/state values that changed between renders. For hooks, DevTools tries to detect which ones may been related to the update by comparing prev/next internal hook structures.
My initial implementation tried to detect all changed hooks. In hindsight this is confusing, because only stateful hooks (e.g. useState, useReducer, and useSyncExternalStore) can schedule an update. (Other types of hooks can change between renders, but in a reactive way.) This PR changes the behavior to only report hooks that scheduled the update.
* Move createRoot/hydrateRoot to /client
We want these APIs ideally to be imported separately from things you
might use in arbitrary components (like flushSync). Those other methods
are "isomorphic" to how the ReactDOM tree is rendered. Similar to hooks.
E.g. importing flushSync into a component that only uses it on the client
should ideally not also pull in the entry client implementation on the
server.
This also creates a nicer parity with /server where the roots are in a
separate entry point.
Unfortunately, I can't quite do this yet because we have some legacy APIs
that we plan on removing (like findDOMNode) and we also haven't implemented
flushSync using a flag like startTransition does yet.
Another problem is that we currently encourage these APIs to be aliased by
/profiling (or unstable_testing). In the future you don't have to alias
them because you can just change your roots to just import those APIs and
they'll still work with the isomorphic forms. Although we might also just
use export conditions for them.
For that all to work, I went with a different strategy for now where the
real API is in / but it comes with a warning if you use it. If you instead
import /client it disables the warning in a wrapper. That means that if you
alias / then import /client that will inturn import the alias and it'll
just work.
In a future breaking changes (likely when we switch to ESM) we can just
remove createRoot/hydrateRoot from / and move away from the aliasing
strategy.
* Update tests to import from react-dom/client
* Fix fixtures
* Update warnings
* Add test for the warning
* Update devtools
* Change order of react-dom, react-dom/client alias
I think the order matters here. The first one takes precedence.
* Require react-dom through client so it can be aliased
Co-authored-by: Andrew Clark <git@andrewclark.io>
There was a bug that occurred when a destroy effect is called that causes an update. The update would be added to the updaters list even though the fiber that was calling the destroy effect was unmounted and no longer exists. This PR:
* Adds a patch to Devtools to filter out all in the update list that aren't in the fiberToIDMap (which contains all fibers currently on screen)
* Enable prefer-const rule
Stylistically I don't like this but Closure Compiler takes advantage of
this information.
* Auto-fix lints
* Manually fix the remaining callsites
Andrew Clark