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## Motivation

An *interleaved* update is one that is scheduled while a render is
already in progress, typically from a concurrent user input event.

We have to take care not to process these updates during the current
render, because a multiple interleaved updates may have been scheduled
across many components; to avoid tearing, we cannot render some of
those updates without rendering all of them.

## Old approach

What we currently do when we detect an interleaved update is assign a
lane that is not part of the current render.

This has some unfortunate drawbacks. For example, we will eventually run
out of lanes at a given priority level. When this happens, our last
resort is to interrupt the current render and start over from scratch.
If this happens enough, it can lead to starvation.

More concerning, there are a suprising number of places that must
separately account for this case, often in subtle ways. The maintenance
complexity has led to a number of tearing bugs.

## New approach

I added a new field to the update queue, `interleaved`. It's a linked
list, just like the `pending` field. When an interleaved update is
scheduled, we add it to the `interleaved` list instead of `pending`.

Then we push the entire queue object onto a global array. When the
current render exits, we iterate through the array of interleaved queues
and transfer the `interleaved` list to the `pending` list.

So, until the current render has exited (whether due to a commit or an
interruption), it's impossible to process an interleaved update, because
they have not yet been enqueued.

In this new approach, we don't need to resort to clever lanes tricks to
avoid inconsistencies. This should allow us to simplify a lot of the
logic that's currently in ReactFiberWorkLoop and ReactFiberLane,
especially `findUpdateLane` and `getNextLanes`. All the logic for
interleaved updates is isolated to one place.
f15f8f6

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README.md

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 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:

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 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 which have a relatively limited scope. This is a great place to get started.

License

React is MIT licensed.