Andrew ClarkandGitHub
cc24d0ea56
If React finishes rendering a tree, delays committing it (e.g. Suspense), then subsequently starts over or renders a new tree, the pending tree is no longer valid. That's because rendering a new work-in progress mutates the old one in place. The current structure of the work loop makes this hard to reason about because, although `renderRoot` and `commitRoot` are separate functions, they can't be interleaved. If they are interleaved by accident, it either results in inconsistent render output or invariant violations that are hard to debug. This commit adds an invariant that throws if the new tree is the same as the old one. This won't prevent all bugs of this class, but it should catch the most common kind. To implement the invariant, I store the finished tree on a field on the root. We already had a field for this, but it was only being used for the unstable `createBatch` feature. A more rigorous way to address this type of problem could be to unify `renderRoot` and `commitRoot` into a single function, so that it's harder to accidentally interleave the two phases. I plan to do something like this in a follow-up.
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!