Defining formats while retaining methods that updates JS Array

When using a templates that enables the user to edit values in a grid, one need to use the following code to ensure that the changes are also made to the JS Array:
obj.getDataText = function(i, j){return myData[i][j]};
obj.setDataText = function(value, i, j){myData[i][j] = value};

But what if you want to define formats for the various columns:
var str = new Active.Formats.String;
var date = new Active.Formats.Date;
var number = new Active.Formats.Number;
date.setDataFormat("auto");
date.setTextFormat("yyyy/mm/dd");
date.setErrorText("");
number.setTextFormat("###");
number.setErrorText("");

var formats = [number, number, number, number, number, number, str, str, str, str, str, str, date, date, str];

Normally one apply the above defined formats like so:
obj.setDataText(function(i, j){return obj[j].dataToText(myData[i][j])});
obj.setDataValue(function(i, j){return formats[j].dataToValue(myData[i][j])});

How will one apply the formats while retaining the ability to have changes saved to the JS Array

Sorry, that last block of code should read:
obj.setDataText(function(i, j){return formats[j].dataToText(myData[i][j])});
obj.setDataValue(function(i, j){return formats[j].dataToValue(myData[i][j])});