Format currency in javascript

function formatCurrency(fld, curPrefix) {
	//Get rid of any thing other than numbers and decimal places.
 
	if(fld.value == ""){
	}
	else
	{
		num = fld.value;
		num = num.toString().replace(/[^0-9.]/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));
		}
 
 
		// Comment next line you do not want 2 decimal places.
		//fld.value =  ( ( (sign)?'':'-') + curPrefix + num + '.' + cents);
		//return (((sign)?'':'-') + curPrefix + num + '.' + cents);
 
		// UnComment next line you do not want 2 decimal places.
		fld.value =  (((sign)?'':'-') + curPrefix + num);
		return (((sign)?'':'-') + curPrefix + num);
	}
 
}