Andrew ClarkandGitHub
ec652f4daf
* Bugfix: Expiring a partially completed tree (#17926)
* Failing test: Expiring a partially completed tree
We should not throw out a partially completed tree if it expires in the
middle of rendering. We should finish the rest of the tree without
yielding, then finish any remaining expired levels in a single batch.
* Check if there's a partial tree before restarting
If a partial render expires, we should stay in the concurrent path
(performConcurrentWorkOnRoot); we'll stop yielding, but the rest of the
behavior remains the same.
We will only revert to the sync path (performSyncWorkOnRoot) when
starting on a new level.
This approach prevents partially completed concurrent work from
being discarded.
* New test: retry after error during expired render
* Regression: Expired partial tree infinite loops
Adds regression tests that reproduce a scenario where a partially
completed tree expired then fell into an infinite loop.
The code change that exposed this bug made the assumption that if you
call Scheduler's `shouldYield` from inside an expired task, Scheduler
will always return `false`. But in fact, Scheduler sometimes returns
`true` in that scenario, which is a bug.
The reason it worked before is that once a task timed out, React would
always switch to a synchronous work loop without checking `shouldYield`.
My rationale for relying on `shouldYield` was to unify the code paths
between a partially concurrent render (i.e. expires midway through) and
a fully concurrent render, as opposed to a render that was synchronous
the whole time. However, this bug indicates that we need a stronger
guarantee within React for when tasks expire, given that the failure
case is so catastrophic. Instead of relying on the result of a dynamic
method call, we should use control flow to guarantee that the work is
synchronously executed.
(We should also fix the Scheduler bug so that `shouldYield` always
returns false inside an expired task, but I'll address that separately.)
* Always switch to sync work loop when task expires
Refactors the `didTimeout` check so that it always switches to the
synchronous work loop, like it did before the regression.
This breaks the error handling behavior that I added in 5f7361f (an
error during a partially concurrent render should retry once,
synchronously). I'll fix this next. I need to change that behavior,
anyway, to support retries that occur as a result of `flushSync`.
* Retry once after error even for sync renders
Except in legacy mode.
This is to support the `useOpaqueReference` hook, which uses an error
to trigger a retry at lower priority.
* Move partial tree check to performSyncWorkOnRoot
* Factor out render phase
Splits the work loop and its surrounding enter/exit code into their own
functions. Now we can do perform multiple render phase passes within a
single call to performConcurrentWorkOnRoot or performSyncWorkOnRoot.
This lets us get rid of the `didError` field.
React · 
React is a JavaScript library for building user interfaces.
- Declarative: React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes. Declarative views make your code more predictable, simpler to understand, and easier to debug.
- Component-Based: Build encapsulated components that manage their own state, then compose them to make complex UIs. Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep state out of the DOM.
- Learn Once, Write Anywhere: We don't make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code. React can also render on the server using Node and power mobile apps using React Native.
Learn how to use React in your own project.
Installation
React has been designed for gradual adoption from the start, and you can use as little or as much React as you need:
- Use Online Playgrounds to get a taste of React.
- Add React to a Website as a
<script>tag in one minute. - Create a New React App if you're looking for a powerful JavaScript toolchain.
You can use React as a <script> tag from a CDN, or as a react package on npm.
Documentation
You can find the React documentation on the website.
Check out the Getting Started page for a quick overview.
The documentation is divided into several sections:
You can improve it by sending pull requests to this repository.
Examples
We have several examples on the website. Here is the first one to get you started:
function HelloMessage({ name }) {
return <div>Hello {name}</div>;
}
ReactDOM.render(
<HelloMessage name="Taylor" />,
document.getElementById('container')
);
This example will render "Hello Taylor" into a container on the page.
You'll notice that we used an HTML-like syntax; we call it JSX. JSX is not required to use React, but it makes code more readable, and writing it feels like writing HTML. If you're using React as a <script> tag, read this section on integrating JSX; otherwise, the recommended JavaScript toolchains handle it automatically.
Contributing
The main purpose of this repository is to continue to evolve React core, making it faster and easier to use. Development of React happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving React.
Code of Conduct
Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.
Contributing Guide
Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React.
Good First Issues
To help you get your feet wet and get you familiar with our contribution process, we have a list of good first issues that contain bugs which have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.