1function formatToCurrency(amount){
2    return (amount).toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,'); 
3}
4formatToCurrency(12.34546); //"12.35"
5formatToCurrency(42345255.356); //"42,345,255.36"

1(1234567.8).toFixed(2).replace(/(\d)(?=(\d{2})+\d\.)/g, '$1,') // "12,34,567.80"

1Steven Jasper C

1    var x=12345678;
2    x=x.toString();
3    var lastThree = x.substring(x.length-3);
4    var otherNumbers = x.substring(0,x.length-3);
5    if(otherNumbers != '')
6        lastThree = ',' + lastThree;
7    var res = otherNumbers.replace(/\B(?=(\d{2})+(?!\d))/g, ",") + lastThree;
8    alert(res);