Change it to this:
var email = /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i;
This is a regular expression literal that is passed the i
flag which means to be case insensitive.
Keep in mind that email address validation is hard (there is a 4 or 5 page regular expression at the end of Mastering Regular Expressions demonstrating this) and your expression certainly will not capture all valid e-mail addresses.