This Project Is Deprecated

React Hot Loader 3 is on the horizon, and you can try it today (boilerplate branch, upgrade example). It fixes some long-standing issues with both React Hot Loader and React Transform, and is intended as a replacement for both. The docs are not there yet, but they will be added before the final release. For now, this commit is a good reference.

babel-plugin-react-transform

🚀 Now with Babel 6 support (thank you @thejameskyle!)

This plugin wraps React components with arbitrary transforms. In other words, it allows you to instrument React components in any way—limited only by your imagination.

🚧🚧🚧🚧🚧

This is highly experimental tech. If you’re enthusiastic about hot reloading, by all means, give it a try, but don’t bet your project on it. Either of the technologies it relies upon may change drastically or get deprecated any day. You’ve been warned 😉 .

This technology exists to prototype next-generation React developer experience. Please don’t use it blindly if you don’t know the underlying technologies well. Otherwise you are likely to get disillusioned with JavaScript tooling.

No effort went into making this user-friendly yet. The goal is to eventually kill this technology in favor of less hacky technologies baked into React. These projects are not long term.

Ecosystem
Demo Project
Installation
Writing Transforms

Ecosystem

For a reference implementation, see react-transform-boilerplate.
For a starter kit to help write your own transforms, see react-transform-noop.

Transforms

react-transform-hmr - enables hot reloading using HMR API
react-transform-catch-errors - catches errors inside render()
react-transform-debug-inspector - renders an inline prop inspector
react-transform-render-visualizer - highlight components when updated
react-transform-style - support style and className styling for all components
react-transform-log-render - log component renders with passed props and state
react-transform-count-renders - counts how many times your components render

Feeling inspired? Learn how to write transforms and send a PR!

Demo Project

Check out react-transform-boilerplate for a demo showing a combination of transforms.

Installation

This plugin is designed to be used with the Babel 6 ecosystem. These instructions assume you have a working project set up. If you do not have Babel set up in your project, learn how to integrate it with your toolkit before installing this plugin.

Using NPM

Install plugin and save in devDependencies:

npm install --save-dev babel-plugin-react-transform

Install some transforms:

npm install --save-dev react-transform-hmr
npm install --save-dev react-transform-catch-errors

Configuration

Add react-transform to the list of plugins in your babel configuration (usually .babelrc):

{
  "presets": ["react", "es2015"],
  "env": {
    // this plugin will be included only in development mode, e.g.
    // if NODE_ENV (or BABEL_ENV) environment variable is not set
    // or is equal to "development"
    "development": {
      "plugins": [
        // must be an array with options object as second item
        ["react-transform", {
          // must be an array of objects
          "transforms": [{
            // can be an NPM module name or a local path
            "transform": "react-transform-hmr",
            // see transform docs for "imports" and "locals" dependencies
            "imports": ["react"],
            "locals": ["module"]
          }, {
            // you can have many transforms, not just one
            "transform": "react-transform-catch-errors",
            "imports": ["react", "redbox-react"]
          }, {
            // can be an NPM module name or a local path
            "transform": "./src/my-custom-transform"
          }]
          // by default we only look for `React.createClass` (and ES6 classes)
          // but you can tell the plugin to look for different component factories:
          // factoryMethods: ["React.createClass", "createClass"]
        }]
      ]
    }
  }
}

As you can see, each transform, apart from the transform field where you write it name, also has imports and locals fields. You should consult the docs of each individual transform to learn which imports and locals it might need, and how it uses them. You probably already guessed that this is just a way to inject local variables (like module) or dependencies (like react) into the transforms that need them.

Note that when using React.createClass() and allowing babel to extract the displayName property you must ensure that babel-plugin-react-display-name is included before react-transform. See this github issue for more details.

You may optionally specify an array of strings called factoryMethods if you want the plugin to look for components created with a factory method other than React.createClass. Note that you don’t have to do anything special to look for ES6 components—factoryMethods is only relevant if you use factory methods akin to React.createClass.

Writing Transforms

It’s not hard to write a custom transform! First, make sure you call your NPM package react-transform-* so we have uniform naming across the transforms. The only thing you should export from your transform module is a function.

export default function myTransform() {
  // ¯\_(ツ)_/¯
}

This function should return another function:

export default function myTransform() {
  return function wrap(ReactClass) {
    // ¯\_(ツ)_/¯
    return ReactClass;
  }
}

As you can see, you’ll receive ReactClass as a parameter. It’s up to you to do something with it: monkeypatch its methods, create another component with the same prototype and a few different methods, wrap it into a higher-order component, etc. Be creative!

export default function logAllUpdates() {
  return function wrap(ReactClass) {
    const displayName = // ¯\_(ツ)_/¯
    const originalComponentDidUpdate = ReactClass.prototype.componentDidUpdate;

    ReactClass.prototype.componentDidUpdate = function componentDidUpdate() {
      console.info(`${displayName} updated:`, this.props, this.state);

      if (originalComponentDidUpdate) {
        originalComponentDidUpdate.apply(this, arguments);
      }
    }

    return ReactClass;
  }
}

Oh, how do I get displayName? Actually, we give your transformation function a single argument called options. Yes, options:

export default function logAllUpdates(options) {

It contains some useful data. For example, your options could look like this:

{
  // the file being processed
  filename: '/Users/dan/p/my-projects/src/App.js',
  // remember that "imports" .babelrc option?
  imports: [React],
  // remember that "locals" .babelrc option?
  locals: [module],
  // all components declared in the current file
  components: {
    $_MyComponent: {
      // with their displayName when available
      displayName: 'MyComponent'
    },
    $_SomeOtherComponent: {
      displayName: 'SomeOtherComponent',
      // and telling whether they are defined inside a function
      isInFunction: true
    }
  }
}

Of course, you might not want to use all options, but isn’t it nice to know that you have access to them in the top scope—which means before the component definitions actually run? (Hint: a hot reloading plugin might use this to decide whether a module is worthy of reloading, even if it contains an error and no React components have yet been wrapped because of it.)

So, to retrieve the displayName (or isInFunction, when available), use the options parameter and the second uniqueId parameter given to the inner function after ReactClass:

export default function logAllUpdates(options) {
  return function wrap(ReactClass, uniqueId) {
    const displayName = options.components[uniqueId].displayName || '<Unknown>';

This is it!

Sure, it’s a slightly contrived example, as you can grab ReactClass.displayName just fine, but it illustrates a point: you have information about all of the components inside a file before that file executes, which is very handy for some transformations.

Here is the complete code for this example transformation function:

export default function logAllUpdates(options) {
  return function wrap(ReactClass, uniqueId) {
    const displayName = options.components[uniqueId].displayName || '<Unknown>';
    const originalComponentDidUpdate = ReactClass.prototype.componentDidUpdate;

    ReactClass.prototype.componentDidUpdate = function componentDidUpdate() {
      console.info(`${displayName} updated:`, this.props, this.state);

      if (originalComponentDidUpdate) {
        originalComponentDidUpdate.apply(this, arguments);
      }
    }

    return ReactClass;
  }
}

Now go ahead and write your own! Don’t forget to tag it with react-transform keyword on npm.

Patrons

The work on React Transform, React Hot Loader, Redux, and related projects was funded by the community. Meet some of the outstanding companies that made it possible:

See the full list of React Transform patrons.

License

MIT

gaearon/babel-plugin-react-transform

gaearon

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