prototype issue

Hi all,

I'm trying to add a method on the prototype of an object.

I put these objects into an array called changes by doing new Changes.

Then I call the method using:

changes[0].createTable();

Why does it not work?

function Changes ( changedBy, changedOn, changeType, change, changeFrom, changePage, row ) {

    this.changedBy = changedBy;
    this.changedOn = changedOn;
    this.changeType = changeType;
    this.change = change;
    this.changeFrom = changeFrom;
    this.changePage = changePage;
    // use row to control how many rows the table needs
    this.row = row;

}
Changes.prototype.createTable = function () {

    // set the document properties to A4 margin 10mm make the text frame fill  the page
    app.documents.add( );
    var doc = app.activeDocument;

    var textFrame = doc.pages[0].textFrames.add ( {geometricBounds: [12.7,12.7,284.299999999461,197.299999999936] } );

    // add the content to a table
    //if a table exists then add a new row
    }