inherit.js

function inherit(child, parent) {
  child.prototype = Object.create(parent.prototype);
  child.prototype.constructor = child;
}

var Person = function Person(firstName, lastName) {
  if (!firstName || !lastName) throw "Primeiro e último nome requerido!";

  this.firstName = firstName;
  this.lastName = lastName;
}

Person.prototype.fullName = function() {
  return this.firstName + " " + this.lastName;
}

var Ninja = function Ninja(firstName, lastName, stars) {
  Person.call(this, firstName, lastName); // super
  this.stars = 10;
}

// Note que eu herdei antes de definir o resto das funções
// no prototype do Ninja.
inherit(Ninja, Person);

Ninja.prototype.throwStar = function(first_argument) {
  this.stars -= 1;
  return "Star throwed";
}