Rubén Norte
b1040c4e46
Summary: Pull Request resolved: https://github.com/facebook/react-native/pull/38100 This creates an experimental subset of MutationObserver. This will not be available yet and is only compatible with the new React Native architecture. This shouldn't show up in the changelog until we're ready to enable this in some form. Changelog: [Internal] ## Context This implements a subset of the `MutationObserver` API (as defined on the Web) for React Native. This subset allows observing nodes added or removed from the UI tree (at any depth) without modifications in user code. This is not possible at the moment and it's required by some performance logging APIs that rely on observability for tracking. **This is not intended for general use at the moment**. We will continue experimenting with this API and might change important details about how it works. ## Implementation details This API is implemented as a native module that registers a commit hook in Fabric. Whenever there's a commit in React Native, we check for nodes added or removed from the shadow tree (compared with the previous committed version). **This implementation is completely cross-platform.** This API uses a centralized entity in JS and native to handle registration of observers and dispatch of notifications. The dispatch the notifications for all observers in the same callback so we can easily change the sequencing of events easily (for example, we can change this to use microtasks when they're available in RN). An important aspect to highlight about this is that we call into JavaScript when executing the commit hooks. **We assume that commit hooks that trigger mutations will always happen in the JS thread**, so it's safe to do so. This was necessary because React nullifies all fields in fiber when they're unmounted, and we're reporting nodes being deleted. If we wait too long to get a reference to the public instances, they become unavailable and this API doesn't work correctly. To avoid this we eagerly get references to these public instances right when mutations are being applied, so it's safe. ## Known limitations * Only the `childList` and `subtree` options are supported. * There is a feature flag in React Native to do commits in background threads to avoid having to do that work in JS (including layout). This implementation is NOT compatible with that and we're currently working on removing the background executor permanently. * Notifications from `MutationObserver` are dispatched as regular JavaScript tasks, not as microtasks, and they don't block rendering/mount/paint. Some consequences of that are: * UI changes done in MutationObserver callbacks are not flushed atomically with the changes being observed. This is caused by the lack of microtasks and because Fabric doesn't wait for them to mount commits in the host platform. * MutationObserver callbacks cannot reliably set up intersection observers to get a notification for the first paint, as it could have potentially happened already (similar to the previous point). We are working on infrastructure changes (support for microtasks, blocking paint on microtasks, etc.) to overcome this limitations. ---- Reviewed By: sammy-SC Differential Revision: D46149086 fbshipit-source-id: be7ba4acd0886d1661a6500d61d2122f34b98b5a
React Native
Learn once, write anywhere:
Build mobile apps with React.
Getting Started · Learn the Basics · Showcase · Contribute · Community · Support
React Native brings React's declarative UI framework to iOS and Android. With React Native, you use native UI controls and have full access to the native platform.
- Declarative. React makes it painless to create interactive UIs. Declarative views make your code more predictable and easier to debug.
- Component-Based. Build encapsulated components that manage their state, then compose them to make complex UIs.
- Developer Velocity. See local changes in seconds. Changes to JavaScript code can be live reloaded without rebuilding the native app.
- Portability. Reuse code across iOS, Android, and other platforms.
React Native is developed and supported by many companies and individual core contributors. Find out more in our ecosystem overview.
Contents
- Requirements
- Building your first React Native app
- Documentation
- Upgrading
- How to Contribute
- Code of Conduct
- License
📋 Requirements
React Native apps may target iOS 13.4 and Android 5.0 (API 21) or newer. You may use Windows, macOS, or Linux as your development operating system, though building and running iOS apps is limited to macOS. Tools like Expo can be used to work around this.
🎉 Building your first React Native app
Follow the Getting Started guide. The recommended way to install React Native depends on your project. Here you can find short guides for the most common scenarios:
📖 Documentation
The full documentation for React Native can be found on our website.
The React Native documentation discusses components, APIs, and topics that are specific to React Native. For further documentation on the React API that is shared between React Native and React DOM, refer to the React documentation.
The source for the React Native documentation and website is hosted on a separate repo, @facebook/react-native-website.
🚀 Upgrading
Upgrading to new versions of React Native may give you access to more APIs, views, developer tools, and other goodies. See the Upgrading Guide for instructions.
React Native releases are discussed in this discussion repo.
👏 How to Contribute
The main purpose of this repository is to continue evolving React Native core. We want to make contributing to this project as easy and transparent as possible, and we are grateful to the community for contributing bug fixes and improvements. Read below to learn how you can take part in improving React Native.
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 Native.
Open Source Roadmap
You can learn more about our vision for React Native in the Roadmap.
Good First Issues
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, gain experience, and get familiar with our contribution process.
Discussions
Larger discussions and proposals are discussed in @react-native-community/discussions-and-proposals.
📄 License
React Native is MIT licensed, as found in the LICENSE file.
React Native documentation is Creative Commons licensed, as found in the LICENSE-docs file.