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An alternative implementation of React.


An alternative implementation of React.


For clarity. The code base is tiny compared to React but React's core functionality is nonetheless implemented faithfully, as far as it goes. It led to a greater appreciation of React.

Reverse Engineering React

There is now a series of complementary videos:

Reverse Engineering React


  • The toArray() helper method is now called guaranteeArray().
  • The index variable in the indexOf() helper method is now initially set to null.
  • The remount() method of the ReactElement should call the getChildContext() method.
  • The libES2015 directories in both the root and examples directories have been renamed es6.
  • Component state has been put back by popular demand.
  • The examples have been moved to the es6 folder.


With npm:

npm install reaction

You can also clone the repository with Git...

git clone

...then install the necessary modules with npm from within the project's root directory:

npm install

You will need to do this if you want to look at the examples.


Launch the examples.html file in the project's root directory. There is a Redux as well as a vanilla example application.


var reaction = require('reaction'),
    ReactDOM = reaction.ReactDOM,
    React = reaction.React;

Now just write your JSX and React code in the normal way, although bear in mind only subset of React's functionality is supported.

Compiling from source

Automation is thanks to npm scripts, have a look at the package.json file. The pertinent commands are:

npm run build-debug
npm run watch-debug

Supported functionality

  • React classes
  • React components
  • React functions
  • References
  • Contexts
  • Mounting and unmounting

Contexts are handled slightly differently. React elements can only pass down a context to child elements, and those child elements can only receive a context, in its entirety. However, the current context is available as this.context when the getChildContext() method is invoked, or passed as the second argument of the getChildContext() method in the case of functions, so you can make programmatic decisions about what context to pass down to children.

Functionality that is not supported

  • Of the component lifecycle, all methods except componentDidMount() and componentWillUnmount() are not supported.