prototype-chain.js

var Animal = function(name){
  this.name = name;
};

Animal.prototype.speak = function(){
  console.log(this.name);
};

var Dog = function(name){
  Animal.call(this, name);
};

Dog.prototype = Object.create(Animal.prototype);

Dog.prototype.speak = function(){
  console.log('woof');
};

var pup = new Dog('fido');
pup.speak();