preactjs/preact-compat

ATTENTION: preact-compat has moved to the main repo.

The code here is only meant for the older Preact 8.x release line. If you're still on Preact 8.x we highly recommend upgrading to the 10.x release line as it includes significant improvements and a much more stable React compatibility layer.

🚨 Note: This module is for Preact 8.x and prior - Preact X includes compat by default. For Preact X, please uninstall preact-compat and replace your aliases with preact/compat.

This module is a compatibility layer that makes React-based modules work with Preact, without any code changes.

It provides the same exports as react and react-dom, meaning you can use your build tool of choice to drop it in where React is being depended on.

Interested? Here's an example project that uses preact-compat to work with an existing React library unmodified, achieving more than 95% reduction in size:

preact-compat-example

---

Why?

... or really, "why preact"?

React is a great library and a great concept, and has a large community of module authors creating high-quality components. However, these components are tightly coupled to React through the use of generic package imports (example).

Preact is a tiny (3kb) implementation of the core value of React, and maintains a nearly identical API. With a shim like this in place, it is possible to use other React-like libraries like Preact, without forking modules just to change their imports.

There are better long-term ways to solve the coupling issue, like using factory functions that accept named generic methods (not just React DI), as suggested by Eric Elliot. However, since the React community has already authored so many modules in a more explicitly coupled manner, it's worth having a simple short-term solution for those who would like to liberate themselves from library lock-in.

---

Installation

You need to install preact-compat first through npm:

npm i --save preact-compat

NOTE: You need to have preact already installed, if you don't, install it like so:

npm i --save preact

Usage with Webpack

Using preact-compat with Webpack is easy.

All you have to do is add an alias for react and react-dom:

{
    // ...
    resolve: {
        alias: {
            'react': 'preact-compat',
            'react-dom': 'preact-compat',
            // Not necessary unless you consume a module using `createClass`
            'create-react-class': 'preact-compat/lib/create-react-class',
            // Not necessary unless you consume a module requiring `react-dom-factories`
            'react-dom-factories': 'preact-compat/lib/react-dom-factories'
        }
    }
    // ...
}

Usage with Browserify

Using preact-compat with Browserify is as simple as installing and configuring aliasify.

First, install it: npm install --save-dev aliasify

... then in your package.json, configure aliasify to alias react and react-dom:

{
    // ...
    "aliasify": {
        "aliases": {
            "react": "preact-compat",
            "react-dom": "preact-compat",
            // Not necessary unless you consume a module using `createClass`
            "create-react-class": "preact-compat/lib/create-react-class",
            // Not necessary unless you consume a module requiring `react-dom-factories`
            "react-dom-factories": "preact-compat/lib/react-dom-factories"
        }
    }
    // ...
}

If you want to use a package that has a peer dependency of React and want it to point to preact-compat you’ll need to set Aliasify to be a global transform. This is not achievable by editing package.json, you’ll need to use the Browserify api and include the global option there:

b.transform(aliasify, {
  global: true,
  aliases: {
    'react': 'preact-compat',
    'react-dom': 'preact-compat'
  }
});

Usage with Babel

Using preact-compat with Babel is easy.

Install the babel plugin for aliasing: npm install --save-dev babel-plugin-module-resolver

All you have to do is tell babel to process jsx with 'h' and add an alias for react and react-dom in your .babelrc:

{
    // ...
    "plugins": [
        ["module-resolver", {
        "root": ["."],
        "alias": {
            "react": "preact-compat",
            "react-dom": "preact-compat",
            // Not necessary unless you consume a module using `createClass`
            "create-react-class": "preact-compat/lib/create-react-class",
            // Not necessary unless you consume a module requiring `react-dom-factories`
            "react-dom-factories": "preact-compat/lib/react-dom-factories"
        }
        }]
    ],
    "presets": [
        "react"
    ]
    // ...
}

Usage with Brunch

Using preact-compat with Brunch requires no extra plugins.

In your brunch-config.js you can export an npm object to configure aliases:

// ...
exports.npm = {
  enabled: true,
  aliases: {
    'react': 'preact-compat',
    'react-dom': 'preact-compat'
  }
}
// ...

Once Aliased

With the above Webpack or Browserify aliases in place, existing React modules should work nicely:

import React, { Component } from 'react';
import { render } from 'react-dom';

class Foo extends Component {
    propTypes = {
        a: React.PropTypes.string.isRequired
    };
    render() {
        let { a, b, children } = this.props;
        return <div {...{a,b}}>{ children }</div>;
    }
}

render((
    <Foo a="a">test</Foo>
), document.body);

---

Use Without Webpack/Browserify

preact-compat and its single dependency prop-types are both published as UMD modules as of preact-compat version 0.6. This means you can use them via a <script> tag without issue:

<script src="//unpkg.com/preact"></script>
<script src="//unpkg.com/prop-types/prop-types.min.js"></script>
<script src="//unpkg.com/preact-compat"></script>
<script>
    var React = preactCompat,
        ReactDOM = preactCompat;
    ReactDOM.render(<h1>Hello!</h1>, document.body);
</script>

You can see the above in action with this JSFiddle Example.

---

PropTypes

preact-compat adds support for validating PropTypes out of the box. This can be disabled the same way it is when using React, by defining a global process.env.NODE_ENV='production'. PropType errors should work the same as in React - the prop-types module used here is published by the React team to replace PropTypes in React.

License

MIT