Sebastian Markbåge
fee786a057
This a follow up to #28564. It's alternative to #28609 which takes #28610 into account. It used to be possible to return JSX from an action with `useActionState`. ```js async function action(errors, payload) { "use server"; try { ... } catch (x) { return <div>Error message</div>; } } ``` ```js const [errors, formAction] = useActionState(action); return <div>{errors}</div>; ``` Returning JSX from an action is itself not anything problematic. It's that it also has to return the previous state to the action reducer again that's the problem. When this happens we accidentally could serialize an Element back to the server. I fixed this in #28564 so it's now blocked if you don't have a temporary reference set. However, you can't have that for the progressive enhancement case. The reply is eagerly encoded as part of the SSR render. Typically you wouldn't have these in the initial state so the common case is that they show up after the first POST back that yields an error and it's only in the no-JS case where this happens so it's hard to discover. As noted in #28609 there's a security implication with allowing elements to be sent across this kind of payload, so we can't just make it work. When an error happens during SSR our general policy is to try to recover on the client instead. After all, SSR is mainly a perf optimization in React terms and it's not primarily intended for a no JS solution. This PR takes the approach that if we fail to generate the progressive enhancement payload. I.e. if the serialization of previous state / closures throw. Then we fallback to the replaying semantics just client actions instead which will succeed. The effect of this is that this pattern mostly just works: - First render in the typical case doesn't have any JSX in it so it just renders a progressive enhanced form. - If JS fails to hydrate or you click early we do a form POST. If that hits an error and it tries to render it using JSX, then the new page will render successfully - however this time with a Replaying form instead. - If you try to submit the form again it'll have to be using JS. Meaning if you use JSX as the error return value of form state and you make a first attempt that fails, then no JS won't work because either the first or second attempt has to hydrate. We have ideas for potentially optimizing away serializing unused arguments like if you don't actually use previous state which would also solve it but it wouldn't cover all cases such as if it was deeply nested in complex state. Another approach that I considered was to poison the prev state if you passed an element back but let it through to the action but if you try to render the poisoned value, it wouldn't work. The downside of this is when to error. Because in the progressive enhancement case it wouldn't error early but when you actually try to invoke it at which point it would be too late to fallback to client replaying. It would probably have to always error even on the client which is unfortunate since this mostly just works as long as it hydrates.
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 Quick Start to get a taste of React.
- Add React to an Existing Project to use as little or as much React as you need.
- Create a New React App if you're looking for a powerful JavaScript toolchain.
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:
- Quick Start
- Tutorial
- Thinking in React
- Installation
- Describing the UI
- Adding Interactivity
- Managing State
- Advanced Guides
- API Reference
- Where to Get Support
- Contributing Guide
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.
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.