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*This API is experimental and subject to change or removal.* This PR is an alternative to https://github.com/facebook/react/pull/32421 based on feedback: https://github.com/facebook/react/pull/32421#pullrequestreview-2625382015 . The difference here is that we traverse from the Fragment's fiber at operation time instead of keeping a set of children on the `FragmentInstance`. We still need to handle newly added or removed child nodes to apply event listeners and observers, so we treat those updates as effects. **Fragment Refs** This PR extends React's Fragment component to accept a `ref` prop. The Fragment's ref will attach to a custom host instance, which will provide an Element-like API for working with the Fragment's host parent and host children. Here I've implemented `addEventListener`, `removeEventListener`, and `focus` to get started but we'll be iterating on this by adding additional APIs in future PRs. This sets up the mechanism to attach refs and perform operations on children. The FragmentInstance is implemented in `react-dom` here but is planned for Fabric as well. The API works by targeting the first level of host children and proxying Element-like APIs to allow developers to manage groups of elements or elements that cannot be easily accessed such as from a third-party library or deep in a tree of Functional Component wrappers. ```javascript import {Fragment, useRef} from 'react'; const fragmentRef = useRef(null); <Fragment ref={fragmentRef}> <div id="A" /> <Wrapper> <div id="B"> <div id="C" /> </div> </Wrapper> <div id="D" /> </Fragment> ``` In this case, calling `fragmentRef.current.addEventListener()` would apply an event listener to `A`, `B`, and `D`. `C` is skipped because it is nested under the first level of Host Component. If another Host Component was appended as a sibling to `A`, `B`, or `D`, the event listener would be applied to that element as well and any other APIs would also affect the newly added child. This is an implementation of the basic feature as a starting point for feedback and further iteration. |
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react-test-renderer (DEPRECATED)
Deprecation notice
react-test-renderer is deprecated and no longer maintained. It will be removed in a future version. As of React 19, you will see a console warning when invoking ReactTestRenderer.create().
React Testing
This library creates a contrived environment and its APIs encourage introspection on React's internals, which may change without notice causing broken tests. It is instead recommended to use browser-based environments such as jsdom and standard DOM APIs for your assertions.
The React team recommends @testing-library/react as a modern alternative that uses standard APIs, avoids internals, and promotes best practices.
React Native Testing
The React team recommends @testing-library/react-native as a replacement for react-test-renderer for native integration tests. This React Native testing-library variant follows the same API design as described above and promotes better testing patterns.
Documentation
This package provides an experimental React renderer that can be used to render React components to pure JavaScript objects, without depending on the DOM or a native mobile environment.
Essentially, this package makes it easy to grab a snapshot of the "DOM tree" rendered by a React DOM or React Native component without using a browser or jsdom.
Documentation: https://reactjs.org/docs/test-renderer.html
Usage:
const ReactTestRenderer = require('react-test-renderer');
const renderer = ReactTestRenderer.create(
<Link page="https://www.facebook.com/">Facebook</Link>
);
console.log(renderer.toJSON());
// { type: 'a',
// props: { href: 'https://www.facebook.com/' },
// children: [ 'Facebook' ] }
You can also use Jest's snapshot testing feature to automatically save a copy of the JSON tree to a file and check in your tests that it hasn't changed: https://jestjs.io/blog/2016/07/27/jest-14.html.