简单的面向对象的JavaScript示例

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?

Answer 1

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;
};