explain.js

var Bar = { bar: ... }
var Foo = { foo: ... }

var Delegate = {
  foo: function() {
    Foo.foo.apply(this, arguments);
  },
  bar: function() {
    Bar.bar.apply(this, arguments);
  }
}

var Composite = extend({}, Bar, Foo);

var Prototype = Object.create(extend(Bar, Foo))