Javascript: currency format function

function formatCurrency(num) {
   num = num.toString().replace(/\$|\,/g,'');
   if(isNaN(num))
   num = "0";
   sign = (num == (num = Math.abs(num)));
   num = Math.floor(num*100+0.50000000001);
   cents = num%100;
   num = Math.floor(num/100).toString();
   if(cents<10)
   cents = "0" + cents;
   for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++)
   num = num.substring(0,num.length-(4*i+3))+','+
   num.substring(num.length-(4*i+3));
   return (((sign)?'':'-') + '$' + num + '.' + cents);
}


Source:
http://javascript.internet.com/forms/currency-format.html