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regenerator Build Status

This package implements a fully-functional source transformation that takes the syntax for generators/yield from ECMAScript 2015 or ES2015 and Asynchronous Iteration proposal and spits out efficient JS-of-today (ES5) that behaves the same way.

A small runtime library (less than 1KB compressed) is required to provide the wrapGenerator function. You can install it either as a CommonJS module or as a standalone .js file, whichever you prefer.


From npm:

npm install -g regenerator

From GitHub:

cd path/to/node_modules
git clone git://
cd regenerator
npm install .
npm test


You have several options for using this module.

Simplest usage:

regenerator es6.js > es5.js # Just the transform.
regenerator --include-runtime es6.js > es5.js # Add the runtime too.
regenerator src lib # Transform every .js file in src and output to lib.

Programmatic usage:

var es5Source = require("regenerator").compile(es6Source).code;
var es5SourceWithRuntime = require("regenerator").compile(es6Source, {
  includeRuntime: true

AST transformation:

var recast = require("recast");
var ast = recast.parse(es6Source);
ast = require("regenerator").transform(ast);
var es5Source = recast.print(ast);

How can you get involved?

The easiest way to get involved is to look for buggy examples using the sandbox, and when you find something strange just click the "report a bug" link (the new issue form will be populated automatically with the problematic code).

Alternatively, you can fork the repository, create some failing tests cases in test/tests.es6.js, and send pull requests for me to fix.

If you're feeling especially brave, you are more than welcome to dive into the transformer code and fix the bug(s) yourself, but I must warn you that the code could really benefit from better implementation comments.