React Hot API

This is a generic library implementing hot reload for React components without unmounting or losing their state.

It is intended for build tool authors or adventurous folk and not for website development. For a reference implementation that you can actually use, check out react-hot-loader for Webpack.

This library drives React hot-reload magic of react-hot-loader but is not tied to Webpack itself, so alternative build systems that support hot-reloading individual modules can use it to implement live-editing for React components. For example, you can use this to integrate hot reloading into an atom-shell application.

See the video.

API

makeHot: (ReactClass, persistentId?) => ReactClass

Registers a hot-reloadable React class. If you don't pass persistentId, it is inferred from ReactClass.displayName or ReactClass.name (for ES6 classes). When called for the first time, it will merely return the passed class. When called the next time with the same persistentId, will patch original class with the prototype of the new class, and return the original class.

require('react-hot-api'): (getRootInstances, React) => makeHot

Invoke this once within each hot-reloadable module to obtain the function described above.
You must pass the result between all emitted versions of the same module for hot reload to work.

getRootInstances is a method you as a caller should provide. It should return all root components on the page. You can implement it by returning require('react/lib/ReactMount')._instancesByReactRootID but you may also want to return some known root instance, for example, if you host React Hot API on a webpage for a live editor playground.

Usage

This library is not meant to be used directly, unless you're authoring a build tool like React Hot Loader.

It only makes sense if your build tool of choice is capable of two things:

• emitting next versions of the same module and evaluate them;
• passing arbitrary JS objects from previous to the next version of the same module.

I am only aware of Webpack Hot Module Replacement but eventually other implementations should arise.

In which case, here's how you can tranform the source to use it:

SomeComponent.js, first run

var React = require('react');

var SomeComponent = React.createClass({
  render: function () {
    return <p>Version 1</p>;
  }
});

module.exports = SomeComponent;



// ================================================
// The code you might generate with your build tool
// to hide hot reloading mechanics from user:

var makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot;
if (!makeHot) {
  // On the first run, we will get here
  makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot = require('react-hot-api')(require('react/lib/ReactMount'));
}

// Will merely register SomeComponent so it can later be patched
module.exports = makeHot(module.exports);

SomeComponent.js, subsequent runs (emitted after user edits the source)

var React = require('react');

var SomeComponent = React.createClass({
  render: function () {
    return <p>Version 2</p>;
  }
});

module.exports = SomeComponent;



// ================================================
// The code you might generate with your build tool
// to hide hot reloading mechanics from user:

var makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot;
if (!makeHot) {
  // On the second run, we will *NOT* get here
  makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot = require('react-hot-api')(require('react/lib/ReactMount'));
}

// Will patch existing SomeComponent with updated methods, force re-rendering and return patched first version
module.exports = makeHot(module.exports);

You may also give user some way to access makeHot in case they want to allow hot-reloading for arbitrary classes inside the module:

AnonComponents.js

// The user still doesn't need to know these lines are being inserted by the tool:
module.makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot;
if (!module.makeHot) {
  // put the function into some sane place (e.g. module.makeHot) without relying on hidden variables
  module.makeHot = SOME_STORAGE_SHARED_BETWEEN_VERSIONS_OF_SAME_MODULE.makeHot = require('react-hot-api')(require('react/lib/ReactMount'));
}
// You might generate the code above with your build tool
// to hide hot reloading mechanics from user.
// ================================================



var React = require('react');

function createLabelComponent(str) {
  var cls = React.createClass({
    render: function () {
      return <span>{str}</span>;
    }
  });
  
  // ... but you may give user freedom to do this:
  if (module.makeHot) { // we're in development and makeHot is available
    cls = module.makeHot(cls, str); // use parameter as unique ID for anon class
  }
  
  return cls;
}

// These will be hot-reloadable:
var Foo = createLabelComponent('Foo');
var Bar = createLabelComponent('Bar');

Thanks

• Tobias Koppers for Webpack and HMR;
• Johannes Lumpe and Ben Alpert for helping me come up with the original hot reloading approach I'm still using here;
• Omar Skalli for coming up with an approach for forcing tree update that is compatible with ES6 classes just the moment I needed it most;
• Kyle Mathews for being the first person to actually use hot loader and helping spread the word when it was in initial stages;
• Christopher Chedeau for retweeting my horrendously hacked together proof of concept video, overwhelming response from which gave me the incentive to actually finish this thing;
• Bret Victor for making me think live editing should be the norm, although he probably hates what people do after watching his videos.