@example_register.js

// This returns a Javascript string
require.registerExtension('.coffee', function(async, source, callback) {
  return compileCoffee(source);
});

// True
require('coffee').test === 123;

// This returns a object
require.registerExtension('.mu', function(async, source, callback) {
  return function () {};
});

// True
typeof require('template') === 'function';

coffee.coffee

exports.test: 123