Question

I have created an object through literals and instantiating using ‘new’ operator. But that’s not working. Here is my code:

var rectangle = { 
    upperLeft : { x : 2, y : 2 },
    lowerRight : { x : 4, y : 4}
}
var r=new rectangle;
alert(r.upperLeft.x) // will yield 2

I have tried using Parentheses after the object name while instantiating:

var r=new rectangle;

But that’s also not working. I have tried creating object using function statement and that’s working fine, but I want to do it this way. Help.

Answer 1

rectangle is, as you noticed, an Object Literal. It’s not a Constructor function, it’s a single instance of Object. If you want rectangle to have more instances, use something like:

function Rectangle(ul,lr){
  var default = {x:0,y:0};
  return {
          upperLeft: ul || default, 
          lowerRight: lr || default 
         };
}

var r1 = new Rectangle({x:2,y:2},{x:4,y:4}),
    r2 = new Rectangle({x:3,y:3},{x:5,y:5}),
    r3 = new Rectangle;

r1.upperleft.x; //=> 2
r2.upperleft.x; //=> 3
r3.upperLeft.x = 5;
r3.upperLeft.y = 7;
alert(r3.upperLeft.x; //=> 5