Flarnie Marchan
15767a8f8f
* Initial failing unit test for error handling in schedule **what is the change?:** see title **why make this change?:** Adding tests for the error handling behavior we are about to add. This test is failing, which gives us the chance to make it pass. Wrote skeletons of some other tests to add. Unit testing this way is really hacky, and I'm also adding to the fixture to test this in the real browser environment. **test plan:** Ran new test, saw it fail! * Add fixture for testing error handling in scheduler **what is the change?:** Added a fixture which does the following - logs in the console to show what happens when you use `requestAnimationFrame` to schedule a series of callbacks and some of them throw errors. Then does the same actions with the `scheduler` and verifies that it behaves in a similar way. Hard to really verify the errors get thrown at the proper time without looking at the console. **why make this change?:** We want the most authentic, accurate test of how errors are handled in the scheduler. That's what this fixture should be. **test plan:** Manually verified that this test does what I expect - right now it's failing but follow up commits will fix that. * Handle errors in scheduler **what is the change?:** We set a flag before calling any callback, and then use a 'try/finally' block to wrap it. Note that we *do not* catch the error, if one is thrown. But, we only unset the flag after the callback successfully finishes. If we reach the 'finally' block and the flag was not unset, then it means an error was thrown. In that case we start a new postMessage callback, to finish calling any other pending callbacks if there is time. **why make this change?:** We need to make sure that an error thrown from one callback doesn't stop other callbacks from firing, but we also don't want to catch or swallow the error because we want engineers to still be able to log and debug errors. **test plan:** New tests added are passing, and we verified that they fail without this change. * Add more tests for error handling in scheduler **what is the change?:** Added tests for more situations where error handling may come up. **why make this change?:** To get additional protection against this being broken in the future. **test plan:** Ran new tests and verified that they fail when error handling fails. * callSafely -> callUnsafely * Fix bugs with error handling in schedule **what is the change?:** - ensure that we properly remove the callback from the linked list, even if it throws an error and is timed out. - ensure that you can call 'cancelScheduledWork' more than once and it is idempotent. **why make this change?:** To fix bugs :) **test plan:** Existing tests pass, and we'll add more tests in a follow up commit. * Unit tests for error handling with timed out callbacks **what is the change?:** More unit tests, to cover behavior which we missed; error handling of timed out callbacks. **why make this change?:** To protect the future!~ **test plan:** Run the new tests. * Adds fixture to test timed out callbacks with scheduler **what is the change?:** See title In the other error handling fixture we compare 'scheduleWork' error handling to 'requestAnimationFrame' and try to get as close as possible. There is no 'timing out' feature with 'requestAnimationFrame' but effectively the 'timing out' feature changes the order in which things are called. So we just changed the order in the 'requestAnimationFrame' version and that works well for illustrating the behavior we expect in the 'scheduleWork' test. **why make this change?:** We need more test coverage of timed out callbacks. **test plan:** Executed the fixture manually in Firefox and Chrome. Results looked good. * fix rebase problems * make fixture compensate for chrome JS speed * ran prettier * Remove 'cancelled' flag on callbackConfig in scheduler, add test **what is the change?:** - Instead of using a 'cancelled' flag on the callbackConfig, it's easier to just check the state of the callbackConfig inside 'cancelScheduledWork' to determine if it's already been cancelled. That way we don't have to remember to set the 'cancelled' flag every time we call a callback or cancel it. One less thing to remember. - We added a test for calling 'cancelScheduledWork' more than once, which would have failed before. Thanks @acdlite for suggesting this in code review. :) **why make this change?:** To increase stability of the schedule module, increase test coverage. **test plan:** Existing tests pass and we added a new test to cover this behavior. * fix typo
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.
Documentation
You can find the React documentation on the website.
It 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:
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.
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.