bf449ee74e
We used to have Event Replaying for any kind of Discrete event where we'd track any event after hydrateRoot and before the async code/data has loaded in to hydrate the target. However, this didn't really work out because code inside event handlers are expected to be able to synchronously read the state of the world at the time they're invoked. If we replay discrete events later, the mutable state around them like selection or form state etc. may have changed. This limitation doesn't apply to Client Actions: - They're expected to be async functions that themselves work asynchronously. They're conceptually also in the "navigation" events that happen after the "submit" events so they're already not synchronously even before the first `await`. - They're expected to operate mostly on the FormData as input which we can snapshot at the time of the event. This PR adds a bit of inline script to the Fizz runtime (or external runtime) to track any early submit events on the page - but only if the action URL is our placeholder `javascript:` URL. We track a queue of these on `document.$$reactFormReplay`. Then we replay them in order as they get hydrated and we get a handle on the Client Action function. I add the runtime to the `bootstrapScripts` phase in Fizz which is really technically a little too late, because on a large page, it might take a while to get to that script even if you have displayed the form. However, that's also true for external runtime. So there's a very short window we might miss an event but it's good enough and better than risking blocking display on this script. The main thing that makes the replaying difficult to reason about is that we can have multiple instance of React using this same queue. This would be very usual but you could have two different Reacts SSR:ing different parts of the tree and using around the same version. We don't have any coordinating ids for this. We could stash something on the form perhaps but given our current structure it's more difficult to get to the form instance in the commit phase and a naive solution wouldn't preserve ordering between forms. This solution isn't 100% guaranteed to preserve ordering between different React instances neither but should be in order within one instance which is the common case. The hard part is that we don't know what instance something will belong to until it hydrates. So to solve that I keep everything in the original queue while we wait, so that ordering is preserved until we know which instance it'll go into. I ended up doing a bunch of clever tricks to make this work. These could use a lot more tests than I have right now. Another thing that's tricky is that you can update the action before it's replayed but we actually want to invoke the old action if that happens. So we have to extract it even if we can't invoke it right now just so we get the one that was there during hydration.
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 the 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 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:
import { createRoot } from 'react-dom/client';
function HelloMessage({ name }) {
return <div>Hello {name}</div>;
}
const root = createRoot(document.getElementById('container'));
root.render(<HelloMessage name="Taylor" />);
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 evolving 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 that have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.