Functional and Pseudoclassical subclasses

subclass.js

//==================================
// Functional classes
// Define methods inside the object constructing function

var makeAnimal = function(name){
  var obj = {};
  obj.name = name;
  var privateVar = ' you can see me';
  
  obj.speak = function () {
    //privateVar is accessible through closure
    console.log('Hi I am '+ obj.name+ privateVar); //Hi I am duck you can see me
  };
  
  return obj;
};

// A functional subclass
var makeWalkingAnimal = function(name, legNum) {
  var obj = makeAnimal(name); //calling the superclass
  obj.legNum = legNum;
  var oldSpeak = obj.speak;
  obj.speak = function (age) {
    if (age < 2){
      oldSpeak();
    } else {
      console.log('Hi I am '+ obj.name+ ' I have '+obj.legNum+' legs');
    }
  };
  return obj;
};

var kiwi = makeWalkingAnimal('Gugu',2);
kiwi.speak(1); //"Hi I am Gugu you can see me"
kiwi.speak(2); //"Hi I am Gugu I have 2 legs"



//============= Pseudoclassical Classes =======================
var Animal = function(name){
  //var this = Object.create(Animal.prototype); //added by JS compiler when invoked with 'new'
  this.name = name;

  //return this;   //added by JS compiler when invoked with 'new'
};
// All the JS functions by default have the prototype property for aggregating methods
Animal.prototype.speak = function(){
  
  console.log('Hi I am', this.name); //Hi I am Butter
};

// A functional subclass
var FlyingAnimal = function(name) {
  //var this = Object.create(FlyingAnimal.prototype); //added by JS compiler when invoked with 'new'
  //we dont want to invoke Animal() with 'new' keyword
  //we still want the property assignment from superclass
  Animal.call(this, name);

  //return this;
};
//establish the prototypal chains so that failed method lookups gets delegated
FlyingAnimal.prototype = Object.create(Animal.prototype);
FlyingAnimal.prototype.speak = function (age) {
    if (age < 2){
      Animal.prototype.speak.call(this);
    } else {
      console.log('Hi I am '+ this.name+ ' I can fly');
    }
};
FlyingAnimal.prototype.constructor = FlyingAnimal;

var butterfly = new FlyingAnimal('Buttter',2);
butterfly.speak(1); //"Hi I am Buttter"
butterfly.speak(2); //"Hi I am Buttter I can fly"