Need JavaScript to Reference another Textfield, but only need first 2 characters to show.

I am creating a form in Adobe Pro X and when info is entered into TextField1, I need the first 2 characters to automatically show up in TextField2.  I have already limited my characters to 2 on TextField2 properties, but need a javascript to reference the TextField1.  If setting the character limit in properties will not work with this javascript, please add that as well.  Thank you.