Andrew Clark
812cf1c6a3
invokeGuardedCallback is a function we use in place of try-catch statement. It accepts a function, and if the function throws, it captures the error. In production, the implementation is a normal try- catch. In development, we swap out the prod implementation for a special version designed to preserve "Pause on all exceptions" behavior of the browser DevTools. invokeGuardedCallbackDev works by dispatching an event to a dummy DOM node and calling the provided function inside a handler for that event. We also attach an error event handler to the window object. If the function throws, the global event handler is called and we can access the error. The global event handler is added and removed right before and after the fake event is dispatched. But if invokeGuardedCallbackDev is nested -- that is, if it's invoked inside the body of another invokeGuardedCallbackDev -- multiple error event handlers will attached simultaneously. We only want the handler that corresponds to the deepest level to handle the error. So we keep track of a depth counter, and within the event handler, we only handle the error if the current depth matches the depth at the time the function was invoked. The problem that we discovered, and that this PR fixes, is that the depth counter is local to each renderer. So if you nest separate copies of invokeGuardedCallback from separate renderers, each renderer will have its own depth counter, and multiple error handlers will fire for a single, nested error.
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.
Examples
We have several examples on the website. Here is the first one to get you started:
class HelloMessage extends React.Component {
render() {
return <div>Hello {this.props.name}</div>;
}
}
ReactDOM.render(
<HelloMessage name="John" />,
document.getElementById('container')
);
This example will render "Hello John" 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. We recommend using Babel with a React preset to convert JSX into native JavaScript for browsers to digest.
Installation
React is available as the react package on npm. It is also available on a CDN.
React is flexible and can be used in a variety of projects. You can create new apps with it, but you can also gradually introduce it into an existing codebase without doing a rewrite.
The recommended way to install React depends on your project. Here you can find short guides for the most common scenarios:
Contributing
The main purpose of this repository is to continue to evolve 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.
Beginner Friendly Bugs
To help you get your feet wet and get you familiar with our contribution process, we have a list of beginner friendly bugs that contain bugs which are fairly easy to fix. This is a great place to get started.
License
React is BSD licensed. We also provide an additional patent grant.
React documentation is Creative Commons licensed.
Examples provided in this repository and in the documentation are separately licensed.