reverse num.toString().replace(/(\d)(?=(\d{3})+(?!\d))/g, '$1 ') code example

Example 1: add comma to number javascript

var n = 34523453.345
n.toLocaleString()
"34,523,453.345"

Example 2: javascript format numbers with commas

function numberWithCommas(x) {
    return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}