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I have this code. It creates an object with x and y field. I want to add a method, which creates new object with additional width and height fields. But despite my tryings it keeps returning undefined. What is wrong?

JSFiddle

function $ (x, y) {
    this.x = x;
    this.y = y;

    return this;
}

$.prototype.$ = function (x, y) {
    this.width = x - this.x;
    this.height = y - this.y;

    return this;
}

var a = $(10,10).$(30,30);
alert(a.width);
share|improve this question
    
When you mention the word "it", to which part of the code are you referring? :) –  summea Apr 26 '13 at 17:41
    
I could not find the correct word (I'm not so good in english, sorry :P) –  Are Wojciechowski Apr 26 '13 at 17:43
    
you show the result of a.width. what about a? is it also undefined? –  Daniel S. Apr 26 '13 at 17:44
    
No problem; just trying to clarify... because "it" could be any part of your code ;) –  summea Apr 26 '13 at 17:45
    
@DanielS. a is defined as an Object. it works now :) –  Are Wojciechowski Apr 26 '13 at 17:46

2 Answers 2

up vote 3 down vote accepted

You missed the new before $; This works:

var a = new $(10,10).$(30,30);
share|improve this answer
    
thanks, silly me. –  Are Wojciechowski Apr 26 '13 at 17:43
up vote 4 down vote 
var a = (new $(10,10)).$(30,30); //You need new
alert(a.width);

Also it might not be a good idea to have an instance function of a class to have the same name as the class -- it is a little confusing.

Here is how you can do what you want to do with 2 "Point" objects (as asked for in the comments):

var Point = (function(){
    var Point = function(x, y) {
        this.width = x;
        this.height = y;
    }
    Point.prototype.removePoint = function(point) {
        return new Point(point.width - this.width, point.height - this.height);
    }

    return Point;
})()

var a = new Point(10,10);
var b = new Point(30,30);

var c = a.removePoint(b);
alert(c.width);

Fiddle: http://jsfiddle.net/maniator/d3fx7/

share|improve this answer
    
It's not when you think about $ as a points. –  Are Wojciechowski Apr 26 '13 at 17:44
    
@AreWojciechowski it is redundant and confusing. It might be a good idea to give actual names to functions :-) –  Neal Apr 26 '13 at 17:45
    
If we are talking about naming now, as well, you may want to avoid using $ for a function (or object) if you start using certain JavaScript libraries out there, as well. –  summea Apr 26 '13 at 17:46
    
@summea a few libraries use $, not only jQuery :-P –  Neal Apr 26 '13 at 17:47
    
@Neal And that is why I wrote the plural form of "library"... ;) (and now the links are updated) –  summea Apr 26 '13 at 17:48

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