How to format number with commas and decimal in Javascript

For example:

1234.542
and you want to format 1,234.54

You can use regular expression to solve the problem.

var value =1234.542
var parts = value.toFixed(2).split(".");
var num = parts[0].replace(/(\d)(?=(\d{3})+(?!\d))/g, "$1,") + 
    (parts[1] ? "." + parts[1] : "");

If you want result 1,234.542 then change toFixed(2) to toFixed(3)