Dan AbramovandGitHub
31487dd82e
* Add a minimal failing test for hot reload * Set up scaffolding for React Fresh * Consider type family when comparing elementType Rendering an element with stale type should not cause it to remount. We only do this for FunctionComponent tag since checking is unnecessary for classes or host components. * Add support for forwardRef() Initially I thought I would compare families of inner .render functions. However, there is a corner case where this can create false positives. Such as when you forwardRef(X) the same X twice. Those are supposed to be distinct. But if we compare .render functions, we wouldn't be able to distinguish them after first reload. It seems safer to rely on explicit registration for those. This should be easy when forwardRef() call is in the same file, and usually it would be. For cases like HOCs and style.div`...` factories that return forwardRef(), we could have the __register__ helper itself "dig deeper" and register the inner function. * Show how forwardRef inner identity can be inferred The __register__ implementation can read the inner identity itself. * Add missing __DEV__ to tests * Add support for memo() (without fixing bailouts) This adds rudimentary support for memo components. However, we don't actually skip bailouts yet, so this is not very useful by itself alone. Tests have TODOs that we need to remove after bailout skipping is done. * Refactor type comparison for clarity * Hot update shouldn't re-render ancestor components unnecessarily My code had a bug where it checked for a wrong thing in a wrong set, leading us to always re-render. This fixes the checks so that we only schedule updates for things that were actually edited. * Add test coverage for memo(fn, areEqual) * Explicitly skip bailouts for hot reloading fibers This forces even memo() with shallow comparison to re-render on hot update. * Refactor scheduling update to reduce duplication * Remove unused variable in test * Don't check presence in a set while not hot reloading * Make scheduleHotUpdate() take named arguments * Don't keep unedited component types in the type => family map It's unnecessary because if they haven't been edited, there's no special reconciliation logic. * Add signatures that force remounting Signatures let us force a remount of a type even if from React's point of view, type is the same. A type has one current signature. If that signature changes during next hot update, all Fibers with that type should be deleted and remounted. We do this by mutating elementType scheduling a parent. This will be handy to force remount of mismatching Hooks, as well as failed error boundaries. For this to fully work, we'll need to add a way to skip built-in bailouts for all Fiber types. This will be the most invasive and annoying change. I did it for HostRoot in this PR but there's more. I'll add an automated test case that catches the missing bailout bailouts. * Support forced remounting for all component types This teaches all parent component types to remount their child if necessary. It also adds tests for them. * Remount effects while preserving state for hot reloaded components This makes sure that changes to *code* always propagate. It can break components that aren't resilient to useEffect over-firing, but that seems like a good constraint since you might need to add a dependency later anyway, and this helps avoid coding yourself into the corner. * Add missing __DEV__ blocks to tests * Fix unused variables in tests * Remove outdated TODO * Expose scheduleHotUpdate directly * Inline isCompatibleType * Run one check per component for invalidating deps This also makes the bailouts more targeted--no need to remount useEffect for a parent component of remounted fiber. * Resolve .type early This moves resolving to set up the right .type early instead of doing this before render. A bit more future-proof in case we want to restructure the begin phase later. ForwardRef is special because its type is a wrapper but it can be hot reloaded by itself. So we have a special overload for it that reconstucts the wrapper type if needed. * Add a Suspense todo * Use current.type !== workInProgress.type for ignoring deps This gets rid of one of the sets. * Use workInProgress.type !== current.type check for force re-render We still use a set for forced remount though. * Use wip.type !== current.type check in more places This also disables the remounting tests. They need a separate approach. * Use a dedicated remount mechanism * Add a test for offscreen trees It has a TODO because it seems like offscreen updates are incorrectly applied too soon. * Enable offscreen test now that it is fixed * Fix corner cases in the new remounting mechanism * Remount failed error boundaries on hot reload * Fix test now that act() flushes This test is manual so I don't actually want act here. * Nits * Add comments
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.