Webmaster Forum / HTML, CSS, Scripts / JavaScript / March 2005

Can someone help me out?

I'm looking for a regular expression that inserts a space
into a string after every fourth byte (except the last).

Specifically, this is to display credit card numbers.

alert(doit("4444555566667777"));

// should return "4444 5555 6666 7777"

function doit(ccno) {
   if (ccno.length % 4 != 0) return;
   var what = ??????
   return what;
}

Here's a non-regular expression approach:

   var what = "";
   for (var i=1; i<ccno.length/4+1; i++) {
       if (what != "") what += " ";
       what += ccno.substring(i*4-4,i*4);
   }

Thanks in advance.