Inheritance

// original classes
function Animal(name, numLegs) {
    this.name = name;
    this.numLegs = numLegs;
    this.isAlive = true;
}
function Penguin(name) {
    this.name = name;
    this.numLegs = 2;
}
function Emperor(name) {
    this.name = name;
    this.saying = "Waddle waddle";
}

// set up the prototype chain
Penguin.prototype = new Animal();
Emperor.prototype = new Penguin();

var myEmperor = new Emperor("Jules");

console.log( myEmperor.saying ); // should print "Waddle waddle"
console.log(  myEmperor.numLegs); // should print 2
console.log(  myEmperor.isAlive); // should print true