oop.js

function extend(Child, Parent) {
  Child.prototype = Object.create(Parent.prototype);
  Child.prototype.constructor = Child;
  return Child;
}

var Message = function (text) {
  this.text = text;
};

Message.prototype.send = function (to) {
  //..
};

var Email = extend(function (text, from, to) {
  //..
}, Message);