ActionScript 2.0 :: Get Date Variables From An Input Box?

I've got a text input box (txt_BirthDay) that I want to enter a date into in the format dd/mm/yyyy.

I want to split the contents of that input box into 3 separate variables for day, week and month.

This works:

Code:
var BirthDay:String = new String(txt_BirthDay.text);
var Day:Number = Number(BirthDay.substr(0,2));
var Month:Number = Number(BirthDay.substr(3,2));
var Year:Number = Number(BirthDay.substr(6,4));
But is it the best way of doing it?

Also, How can I 'mask' the input box so it only accespts inputs in the dd/mm/yyyy format?