Is it possible to make a property in javascript?

Question

I want to make a custom Array object that recieves a number as index, and depending on the value of the index, it would return a computed value.

For example:

>>> var MyArray(2);
>>> MyArray[2];
4
>>> MyArray.2;
4

I know that for the showed example, I'm better of with a function, but I want to know if I can override the properties/index lookup for some things that are conceptualy arrays, but could need some computation.

I'm aware that x.1 == x[1], so what I need is to make a property in javascript.

I mean, make x.variable = x.myPropery(), so everytime that I get the value of x.variable, I recieve the return of x.myPorperty().

Is this even possible?

Answer 1

variable[property] is the same as dot notation so you are doing MyArray.2, which is a variable, not a method that gets evaluated. You can't really do what you want without a method that either changes the property when it is assigned, or a method that computes the right value when you pull it out.

And no, you cannot override [], its simply dot notation, its not really an index that you can override

Re: your comment, Absolutely, you can do

var x = new Array();
x[1] = function () { alert('x') };

var myFunction = x[1];

x[1]();        // alerts "x"
myFunction();  // alerts "x"

alert(x[1]);         // alerts "function () { alert('x') };"
alert(myFunction);   // alerts "function () { alert('x') };"

Answer 2

Currently Javascript Getters and Setters are possible only on

• Firefox
• Safari 3+
• Opera 9.5+

Internet Explorer (in any of it versions) is lacking in this regard.