simple object-oriented JavaScript example

Question

I'm learning OO JavaScript (again). I've written this simple object

function circle(){
  this.radius = 4;
}

circle.prototype.area = function(){
  this.radius * this.radius * 3.14;
};

var c = new circle();
c.area();

The value returned by c.area() is undefined. I guess this can only because this.radius is not returning 4, why not?

By convention, constructors start with a capital letter. By default they return the newly constructed object so you don't need a return statement. But methods must have a return statement if you want them to return a value. — RobG
– RobG, Commented Sep 28, 2011 at 9:15

duri · Accepted Answer · 2011-09-28 08:34:26Z

6

radius has the value of 4, but the area method doesn't return any value.

circle.prototype.area = function(){
  return this.radius * this.radius * 3.14;
};

answered Sep 28, 2011 at 8:34

duri

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4 Comments

RobG Over a year ago

I would add: if (typeof this.area != 'number') this.area = Math.pow(this.radius, 2)*Math.PI; return this.area;.

duri Over a year ago

@RobG I wouldn't. In fact, you'd override the area() method with the area member => area will be callable at the beginning but won't after the first call.

Dónal Over a year ago

@duri thanks, I've been using Groovy for too long (where the return statement is optional)

RobG Over a year ago

@duri - doh, of course! Anyhow, just an exercise for the OP I suspect.

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