react-reconciler

What is react-reconciler?

The react-reconciler package is a framework for building custom React renderers. It provides the core algorithms that React uses for reconciliation, allowing developers to create their own renderers for different target environments beyond what React supports out of the box (e.g., the web or native mobile). This package is an under-the-hood tool primarily intended for advanced use cases where you need to create a custom rendering environment.

What are react-reconciler's main functionalities?

Creating a Custom Renderer

This code sample demonstrates how to start creating a custom renderer using react-reconciler. You define methods like `createInstance` for creating instances of components and `createTextInstance` for handling text. The host config object passed to `ReactReconciler` includes a variety of methods for managing instances, updates, and more.

const MyRenderer = ReactReconciler({
  now: Date.now,
  createInstance: (type, props) => {
    // Create instance of a component
  },
  createTextInstance: (text) => {
    // Create text instance
  },
  // Other host config methods...
});

Scheduling Updates

This example shows how to schedule updates to the container using your custom renderer. The `updateContainer` method is used to apply updates to the container, which in this case is a custom object you manage. This method is part of what allows React's declarative API to work with your custom rendering logic.

const container = {}; // Your container object
MyRenderer.updateContainer(<App />, container, null, () => {
  console.log('Rendered with MyRenderer');
});

Other packages similar to react-reconciler

preact

Preact is a fast 3kB alternative to React with the same modern API. While not a direct alternative to react-reconciler, it offers a different approach to building user interfaces with a smaller footprint. Preact can be used to build custom renderers, but its primary use case is as a React alternative for building web applications.

inferno

Inferno is another high-performance alternative to React that focuses on speed and performance. Similar to Preact, Inferno is not a direct alternative to react-reconciler but offers a different approach to building UIs with an emphasis on performance. Inferno includes its own mechanisms for creating custom renderers, making it a potential alternative for performance-critical applications.

README

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:

• Building a simple custom renderer to DOM
• Building a simple custom renderer to native

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!