gistfile1.js

function Foo(name) {
  this.type = 'foo';
}

Foo.prototype = {
  name: function (name) {
    if (name) {
      this._name = name;
    } else {
      return this._name;
    }
  },
  age: function (age) {
    if (age) {
      this._age = age;
    } else {
      return this._age;
    }
  }
};

function Bar() {
  this.type = 'bar';
}

Bar.prototype = new Foo;
Bar.prototype.size = function () {
  return 'm';
};

var bar = new Bar();

bar.age(32);
alert(bar.age());