Andrew Clark
013b7ad117
* Outline push/pop logic in `renderRoot` I want to get rid of the the `isSync` argument to `renderRoot`, and instead use separate functions for concurrent and synchronous render. As a first step, this extracts the push/pop logic that happens before and after the render phase into helper functions. * Extract `catch` block into helper function Similar to previous commit. Extract error handling logic into a separate function so it can be reused. * Fork `renderRoot` for sync and concurrent Removes `isSync` argument in favor of separate functions. * Extra "root completion" logic to separate function Moving this out to avoid an accidental early return, which would bypass the call to `ensureRootIsScheduled` and freeze the UI. * Inline `renderRoot` Inlines `renderRoot` into `performConcurrentWorkOnRoot` and `performSyncWorkOnRoot`. This lets me remove the `isSync` argument and also get rid of a redundant try-catch wrapper. * [suspense][error handling] Add failing unit test Covers an edge case where an error is thrown inside the complete phase of a component that is in the return path of a component that suspends. The second error should also be handled (i.e. able to be captured by an error boundary. The test is currently failing because there's a call to `completeUnitOfWork` inside the main render phase `catch` block. That call is not itself wrapped in try-catch, so anything that throws is treated as a fatal/unhandled error. I believe this bug is only observable if something in the host config throws; and, only in legacy mode, because in concurrent/batched mode, `completeUnitOfWork` on fiber that throws follows the "unwind" path only, not the "complete" path, and the "unwind" path does not call any host config methods. * [scheduler][profiler] Start time of delayed tasks Fixes a bug in the Scheduler profiler where the start time of a delayed tasks is always 0. * Remove ad hoc `throw` Fatal errors (errors that are not captured by an error boundary) are currently rethrown from directly inside the render phase's `catch` block. This is a refactor hazard because the code in this branch has to mirror the code that happens at the end of the function, when exiting the render phase in the normal case. This commit moves the throw to the end, using a new root exit status. * Handle errors that occur on unwind
react-reconciler
This is an experimental package for creating custom React renderers.
Its API is not as stable as that of React, React Native, or React DOM, and does not follow the common versioning scheme.
Use it at your own risk.
API
const Reconciler = require('react-reconciler');
const HostConfig = {
// You'll need to implement some methods here.
// See below for more information and examples.
};
const MyRenderer = Reconciler(HostConfig);
const RendererPublicAPI = {
render(element, container, callback) {
// Call MyRenderer.updateContainer() to schedule changes on the roots.
// See ReactDOM, React Native, or React ART for practical examples.
}
};
module.exports = RendererPublicAPI;
Practical Examples
A "host config" is an object that you need to provide, and that describes how to make something happen in the "host" environment (e.g. DOM, canvas, console, or whatever your rendering target is). It looks like this:
const HostConfig = {
createInstance(type, props) {
// e.g. DOM renderer returns a DOM node
},
// ...
supportsMutation: true, // it works by mutating nodes
appendChild(parent, child) {
// e.g. DOM renderer would call .appendChild() here
},
// ...
};
For an introduction to writing a very simple custom renderer, check out this article series:
The full list of supported methods can be found here. For their signatures, we recommend looking at specific examples below.
The React repository includes several renderers. Each of them has its own host config.
The examples in the React repository are declared a bit differently than a third-party renderer would be. In particular, the HostConfig object mentioned above is never explicitly declared, and instead is a module in our code. However, its exports correspond directly to properties on a HostConfig object you'd need to declare in your code:
- React ART and its host config
- React DOM and its host config
- React Native and its host config
If these links break please file an issue and we’ll fix them. They intentionally link to the latest versions since the API is still evolving. If you have more questions please file an issue and we’ll try to help!