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## Edit

Went for another approach after talking with @gnoff. The approach is
- add a dev-only error when a precomputed chunk is too big to be written
- suggest to copy it before passing it to `writeChunk`

This PR also includes porting the React Float tests to use the browser
build of Fizz so that we can test it out on that environment (which is
the one used by next).

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## Summary

Someone reported [a bug](vercel/next.js#42466)
in Next.js that pointed to an issue with Node 18 in the streaming
renderer when using importing a CSS module where it only returned a
malformed bootstraping script only after loading the page once.

After investigating a bit, here's what I found:

- when using a CSS module in Next, we go into this code path, which
writes the aforementioned bootstrapping script

- the reason for the malformed script is that
`completeBoundaryWithStylesScript1FullBoth` is emptied after the call to
- it gets emptied in `writeChunk` because we stream the chunk directly
without copying it in this codepath
- the reason why it only happens from Node 18 is because the Webstreams
APIs are available natively from that version and in their
implementation, [`enqueue` transfers the array buffer
thus making it unavailable/empty for subsequent calls. In older Node
versions, we don't encounter the bug because we are using a polyfill in
Next.js, [which does not implement properly the array buffer transfer

I think the proper fix for this is to clone the array buffer before
enqueuing it. (we do this in the other code paths in the function later
on, see ```((currentView: any): Uint8Array).set(bytesToWrite,

## How did you test this change?

Manually tested by applying the change in the compiled Next.js version.

Demonstrate the code is solid. Example: The exact commands you ran and
their output, screenshots / videos if the pull request changes the user
How exactly did you verify that your PR solves the issue you wanted to
  If you leave this empty, your PR will very likely be closed.

Co-authored-by: Sebastian Markbage <>


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React · GitHub license npm version CircleCI Status PRs Welcome

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.


React has been designed for gradual adoption from the start, and you can use as little or as much React as you need:

You can use React as a <script> tag from a CDN, or as a react package on npm.


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.


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.


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.


React is MIT licensed.