Question

In the JavaScript the same thing you can do in many different ways.

Consider the examples:

1:

function Circle(radius) {
 return {
  "r" : radius,
  "area" : function(){
   return Circle.pi * this.r * this.r; 
  }
 }
}
Circle.pi = 3.14159;

var a = Circle(10);
alert(a.area());

2:

function Circle(radius) {
    this.r = radius;
}

Circle.pi = 3.14159;
Circle.prototype.area = function(){
 return Circle.pi * this.r * this.r; 
}

var a = new Circle(10);
alert(a.area());

The second is better than first because we dont define the same function area for any instance of the Circle.

But lets consider
3:

function Circle(radius) {
 return {
  "r" : radius,
  "area" : Circle.area
 }
}
Circle.pi = 3.14159;
Circle.area = function(){
 return Circle.pi * this.r * this.r; 
}

var a = Circle(10);
alert(a.area());

Is there any reason to prefer second style instead of third? Or I misunderstood something at all?

Answer 1

I would definitely go with example 2. Neither example 1 or 3 make good use of JavaScript’s object-oriented features because:

1. You duplicate method definitions in each instance.
2. By returning a new object instead of using this, you lose the identity of the class, i.e. you can no longer do checks like a instanceof Circle.
3. You give up the possibility of inheritance since you do not use prototypes.