inheritance.js

function Animal(name) {
  var self = {};
  self.speak = function() {
    console.log("zzz...");
  };
  self.getName = function() {
    return name;
  };
  return self;
}

function Dog(name) {
  var self = Animal(name);
  self.speak = function() {
    console.log("'Woof!' says " + self.getName());
  };
  return self;
}

var greyBlob = Animal("blob");
greyBlob.speak();

var rover = Dog("rover");
rover.speak();