Andrew Clark
d13f5b9538
Adds a feature flag to tweak the internal heuristic used to "unsuspend" lanes when a new update comes in. A lane is "suspended" if we couldn't finish rendering it because it was missing data, and we chose not to commit the fallback. (In this context, "suspended" does not include updates that finished with a fallback.) When we receive new data in the form of an update, we need to retry rendering the suspended lanes, since the new data may have unblocked the previously suspended work. For example, the new update could navigate back to an already loaded route. It's impractical to retry every combination of suspended lanes, so we need some heuristic that decides which lanes to retry and in which order. The existing heuristic roughly approximates the old Expiration Times model. It unsuspends all lower priority lanes, but leaves higher priority lanes suspended. Then when we start rendering, we choose the lanes that have the highest LanePriority and render those -- and then we add to that all the lanes that are highher priority. If this sounds terribly confusing, it's because it barely makes sense. (It made more sense in the Expiration Times world, I promise, but it was still confusing.) I don't think it's worth me trying to explain the old behavior too much because the point here is that we can replace it with something simpler. The new heurstic is to unsuspend all suspended lanes whenever there's an update. This is effectively what we already do except in a few very specific edge cases, ever since we removed the delayed suspense feature from everything that's not a refresh transition. We can optimize this in the future to only unsuspend lanes that are either 1) in the `lanes` or `subtreeLanes` of the node that was updated, or 2) in the `lanes` of the return path of the node that was updated. This would exclude lanes that are only located in unrelated sibling trees. But, this optimization wouldn't be useful currently because we assign the same transition lane to all transitions. It will become relevant again once we start assigning arbitrary lanes to transitions -- but that in turn requires us to implement entanglement of overlapping transitions, one of our planned projects. So to sum up: the goal here is to remove the weird edge cases and switch to a simpler model, on top of which we can make more substantial improvements. I put it behind a flag so I can run an A/B test and confirm it doesn't cause a regression.
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 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.