CheatSheet: classe e herança de JavaScript

// constructor
var ParentClass = function () {
  // constructor
  this.defaultName = 'Avétis';
};

ParentClass.prototype.sayHelloTo = function (name) {
  console.log('Hi ' + (name || this.defaultName) + '!');
};

var ChildClass = function () {
  // optional, only if you want to call parent constructor
  ChildClass.prototype.constructor.apply(this, arguments);
};

// inheritance
ChildClass.prototype = Object.create(ParentClass.prototype);

ChildClass.prototype.sayHelloTo = function (name) {
  name = name || this.defaultName;
  name = name[0].toUpperCase() + name.slice(1);

  // call parent class method
  ChildClass.prototype.constructor.prototype.sayHelloTo.call(this, name);
};

// instanceof

var a = new ParentClass();
var b = new ChildClass();

console.log(b instanceof ChildClass); // => true
console.log(b instanceof ParentClass); // => true
console.log(a instanceof ChildClass); // => false
console.log(a instanceof ParentClass); // => true


console.log(a.sayHelloTo()); // => "Hi Avétis!"
console.log(b.sayHelloTo()); // => "Hi Avétis!"
console.log(a.sayHelloTo('avetisk')); // => "Hi avetisk!"
console.log(b.sayHelloTo('avetisk')); // => "Hi Avetisk!"

Alguns podem querer adicionar a classe pai ChildClass.__super__ = ParentClasspara facilitar o acesso (o que eu não recomendo).