evanbacon
e37e53086a
Summary:
The React Native community almost exclusively adds `mjs` support with something like: `config.resolver.sourceExts.push("mjs");` which causes `js` to be resolved before `mjs`. Mainstream bundlers will do the opposite, resolving `mjs` then `js`, unless bundling for Node.js environments.
`event-target-shim` has a `.js` and `.mjs` entry, when we [attempt to implement _community-standard_ resolution in Metro](https://github.com/expo/expo/pull/23528) the app fails to open on iOS––providing no indication of what failed. The issue here is that the `mjs` exports for `event-target-shim` don't support `module.exports = function() {}`, so we need to update some of the imports in `react-native` (note that one of the imports to `event-target-shim` already uses `import/export`).
### Discovery
For future readers––to discover this bug, I wrote a custom Metro resolver which printed a list of any `mjs` file that was resolved. In a basic app we observe the following:
```
/node_modules/react-native/Libraries/Core/setUpXHR.js > /node_modules/abort-controller/dist/abort-controller.mjs
/node_modules/react-native/Libraries/Network/XMLHttpRequest.js > /node_modules/event-target-shim/dist/event-target-shim.mjs
/node_modules/react-native/Libraries/WebSocket/WebSocket.js > /node_modules/event-target-shim/dist/event-target-shim.mjs
/node_modules/react-native/Libraries/Blob/FileReader.js > /node_modules/event-target-shim/dist/event-target-shim.mjs
/node_modules/abort-controller/dist/abort-controller.mjs > /node_modules/event-target-shim/dist/event-target-shim.mjs
```
In all cases the mjs files are resolved via `react-native` importing third-party packages, specifically `abort-controller` and `event-target-shim`. I modified the custom Metro resolver to ignore mjs resolution in different files until I found the problematic imports. This revealed that the exports were changing in `event-target-shim` between mjs and js.
Further, this was difficult to discover because the code that attempts to invoke an object as a function (error) is happening during the React Native networking setup. Ideally this JS code would be isolated from the user's bundler configuration and therefore impossible to break.
## Changelog:
[GENERAL] [FIXED] - Update `event-target-shim` import to support Metro resolving `mjs` modules before `js`.
<!-- Help reviewers and the release process by writing your own changelog entry.
Pick one each for the category and type tags:
[ANDROID|GENERAL|IOS|INTERNAL] [BREAKING|ADDED|CHANGED|DEPRECATED|REMOVED|FIXED|SECURITY] - Message
For more details, see:
https://reactnative.dev/contributing/changelogs-in-pull-requests
Pull Request resolved: https://github.com/facebook/react-native/pull/38628
Test Plan:
- If you add `mjs` support to the `metro.config.js` file **before** js (`config.resolver.sourceExts.unshift("mjs");`), the project should be capable of starting.
- Usage with the default `metro.config.js` setup works as well.
- https://github.com/expo/expo/pull/23528 works.
Reviewed By: NickGerleman
Differential Revision: D47816854
Pulled By: TheSavior
fbshipit-source-id: ebaf2e7a3ec02ae61effa004058589053601b766
React Native
Learn once, write anywhere:
Build mobile apps with React.
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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.