Francesco on "[Plugin: Contact Form 7] custom validation"

Hi,

I want to use this javascript to validate a field:

var i=new RegExp("([a-zA-Z0-9]{16}$)");

if(!i.test(frm.code.value)) {
alert("Your code field is empty or it contains non admitted chars");
return false;
}

I put this code in the additional settings but it doesn't work, where am I wrong?

http://wordpress.org/extend/plugins/contact-form-7/