TypeError: window.addEvent is not a function

I am new to chronoforms, and am stumbling upon an error that is probably the cause of my test form not working.
The test form can be found on
http://villapuntacoral2.cloudaccess.net/en/?option=com_chronoforms5&chronoform=Reservation%20Request
I added code to a JavaScript OnLoad handler, which shows or hides a text box when the checkbox is clicked. However, it appears the click event is not registered.
Firefox Console output shows me several errors, one of which is "TypeError: window.addEvent is not a function".

Any ideas what the cause of this would be?

Hi Froefel,

I think that the problem is that you are using MooTools code (which was standard for CFv4 and Joomla! 2.5) with CFv5 on Joomla! 3. These have both switched to use the jQuery library.

You could load MooTools (there's a FAQ to tell you how) but the better solution would be to re-write the script using jQuery :-(

Bob