f1ecf82bfb
We need to optimize the collection of debug info for dev mode. This is an incredibly hot path since it instruments all I/O and Promises in the app. These optimizations focus primarily on the collection of stack traces. They are expensive to collect because we need to eagerly collect the stacks since they can otherwise cause memory leaks. We also need to do some of the processing of them up front. We also end up only using a few of them in the end but we don't know which ones we'll use. The first compromise here is that I now only collect the stacks of "awaits" if they were in a specific request's render. In some cases it's useful to collect them even outside of this if they're part of a sequence that started early. I still collect stacks for the created Promises outside of this though which can still provide some context. The other optimization to awaits, is that since we'll only use the inner most one that had an await directly in userspace, we can stop collecting stacks on a chain of awaits after we find one. This requires a quick filter on a single callsite to determine. Since we now only collect stacks from awaits that belongs to a specific Request we can use that request's specific filter option. Technically this might not be quite correct if that same thing ends up deduped across Requests but that's an edge case. Additionally, I now stop collecting stack for I/O nodes. They're almost always superseded by the Promise that wraps them anyway. Even if you write mostly Promise free code, you'll likely end up with a Promise at the root of the component eventually anyway and then you end up using its stack anyway. You have to really contort the code to end up with zero Promises at which point it's not very useful anyway. At best it's maybe mostly useful for giving a name to the I/O when the rest is just stuff like `new Promise`. However, a possible alternative optimization could be to *only* collect the stack of spawned I/O and not the stack of Promises. The issue with Promises (not awaits) is that we never know what will end up resolving them in the end when they're created so we have to always eagerly collect stacks. This could be an issue when you have a lot of abstractions that end up not actually be related to I/O at all. The issue with collecting stacks only for I/O is that the actual I/O can be pooled or batched so you end up not having the stack when the conceptual start of each operation within the batch started. Which is why I decided to keep the Promise stack.
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.