prototypical inheritance

inheritance.js

var Animal = {
  walk: function() {
    console.log('walk');
  },
  talk: function() {
    console.log('talk');
  }
};
function Dog() {
  this.talk = function() {
    console.log('bark');
  };
};
function Cat() {
  this.talk = function() {
    console.log('meow');
  };
};
Dog.prototype = Animal;
Cat.prototype = Animal;

var dog = new Dog();
dog.walk(); // "walk"
dog.talk(); // "bark"

var cat = new Cat();
cat.walk(); // "walk"
cat.talk(); // "meow"