How to extend/add additional functionality (to) an InDesign class like Cell

Question

Hello,
I am trying to add some extra functionality to every instance of e.g. the Cell 'class' of InDesign using Javascript. I started doing something like this:
Cell.prototype.newFunction = function() { ....... }
which works fine: it is now possible to call newFunction() on every instance of Cell.
But now I would like to let this function (that I've added to the prototype chain of Cell like shown above and thus is also available for an 'instance' of Cell) use a 'variable' that is specific for every Cell instance, e.g.:
Cell.prototype.getSuperValue = function ()
if (this._cachedValue === undefined)
this._cachedValue = 3; // doing some incredible calculations that take some time
return this._cachedValue;
The this._cachedValue should be a attribute of the Cell instance. So if I take to cells from a Table and I call getSuperValue() on them I can get two different values that are specific for every instance of Cell.
Thanks a lot in advance!
P.S. although I am quite new to Javascript I know there are no classes in Javascript and that Cell is an object. But I thought explaining it like this would make it more clear?

Answer 1

Hi John, Harbs and Marc,
Thanks a lot for the helpful information!
One of the things I was trying to do is give the 'instance of Cell' extra functionality like obtaining geometric information of that cell, e.g. getInsideArea which would return a rectangle containing the position and size of that cell. I wanted to give the cell a reference to an Javascript object that contained geometric information of the Table the cell is in. This geometric information is used by me to obtain the cell geometric information.
Again thanks a lot!