Update

Since this post was originally published the 6to5 library was renamed to babel so packages should now use the "use babel"; pragma in their JavaScript files.

See atom/atom#5579 for more details.

Original Post

Starting with yesterday’s 0.177 release, Atom now has built-in support for preprocessing JavaScript files using the 6to5 library.

This allows you to use new ECMAScript 6 features in your packages that aren’t yet implemented in the versions of Chromium and io.js that ship with Atom.

To use this in your packages, make "use 6to5"; the very first line of any .js files you’d like to transform using 6to5. So, for example, here is a package’s main.js file that uses the new ES6 arrow functions:

"use 6to5";

exports.activate   = () => console.log('this package was activated')
exports.deactivate = () => console.log('this package was deactivated')

Since arrow functions aren’t natively supported yet, the code will be converted on-the-fly to:

exports.activate = function () {
  return console.log("this package was activated");
};
exports.deactivate = function () {
  return console.log("this package was deactivated");
};

The 6to5 support uses the same caching strategy that is used for CoffeeScript, CSON, and Less files, so using it in your packages shouldn’t negatively impact startup time.

A huge thanks goes out to Michael Bolin from Facebook, who added this feature. You can check out pull request #5299 for the discussion and implementation details.

Check out the Learn ES6 article on 6to5.org for more information about all the great new ES6 features.