Andrew ClarkandDan Abramov
a650699d2f
* Add DOM fixture for cross-origin errors
* Use a custom error object in place of cross-origin errors
Cross-origin errors aren't accessible by React in DEV mode because we
catch errors using a global error handler, in order to preserve the
"Pause on exceptions" behavior of the DevTools. When this happens, we
should use a custom error object that explains what happened.
For uncaught errors, the actual error message is logged to the console
by the browser, so React should skip logging the message again.
* Add test case that demonstrates errors are logged even if they're caught
* Don't double log error messages in DEV
In DEV, the browser always logs errors thrown inside React components,
even if the originating update is wrapped in a try-catch, because of the
dispatchEvent trick used by invokeGuardedCallback. So the error logger
should not log the message again.
* Fix tests
* Change how error is printed in DEV and PROD
In DEV, we don't want to print the stack trace because the browser already always prints it.
We'll just print the component stack now.
In PROD, we used to omit the JS error message. However we *do* want to show it because
if the application swallows the error, the browser will *not* print it. In DEV it works
only because of the fake event trick. So in PROD we will always print the underlying error
by logging the error object directly. This will show both the message and the JS stack.
* Make the wording tighter and emphasize the real error is above
There's a few goals in the rewording:
* Make it tighter using line breaks between sentences.
* Make it slightly less patronizing ("You should fix it" => "You can find its details in an earlier log")
* ^^ This also helps highlight that the real error message and stack is above
* Group subsections: intro (there's an error), component stack, and final addendum about error boundaries
* ^^ Otherwise people might think error boundaries are part of the reason they have an error
* Make it clear "located at" is not the stacktrace. Otherwise it feels confusing. This makes it clearer you should still look for stack trace (with other details) above and introduces the concept of component stack.
* Make the message shorter
* Unused variables
* Fix an error caused by fixing lint
* One more bikeshed
* Fix fixture
* Remove unused file
* Concise wording
* Unused variables
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.