Acive text entry character limit using Javascript

Hi,

I've been playing around with Articulate Storyline trial version for the past few days, and I've found it to be a fantastic product. That being said, I've run into a problem with text entry boxes.

My goal is to limit the amount of characters that can be put into a text entry, and so far I've been able use the Javascript "subscript" function to get a limit on characters based on Storyline triggers such as when "control loses focus" or "on click". However,  I have not been able to limit the characters while the participant is actively filling out the form.

For example, a participant tries to type "catttttttttt", but since I've set a character limit of 3, I want to make it so that every time they try to type in that extra "t", the user will only see "catt" for a brief moment (or optimally not at all) before the script shortens the input text back to the correct "cat".

I used this resource as the basis of my code : http://javascript.about.com/library/bltxtmax2.htm

I am hoping that someone might be able to explain to me how to use an onkey type function to accomplish this, Since that's what I was intending to use when I first created this script.

Thank you!

Binet Lee