Common module boilerplate that sets export value

a.js

// Define a module "a" that depends another module called "b". If
// that other module also uses this type of boilerplate, then
// in the browser, it will create a global .b that is used below. 

// If you do not want to support the browser global path, then you
// can remove the `root` use and the passing `this` as the first arg to
// the top function.

(function(root, factory) {
  if (typeof exports === 'object') {
    // Node. Does not work with strict CommonJS, but
    // only CommonJS-like enviroments that support module.exports,
    // like Node.
    module.exports = factory(require('b'));
  } else if (typeof define === 'function' && define.amd) {
    // AMD. Register as an anonymous module.
    define(['b'], factory);
  } else {
    // Browser globals
    root.a = factory(root.b);
  }
}(this, function(b) {
  //use b in some fashion.

  //Just return a value to define the module export.
  return {};
}));

Please see the umdjs/umd project for different variations on this kind of boilerplate depending on what you want to support.