Enhancing regex of thousands separator?

Question

I saw this beautiful script to add thousands separator to js numbers:

function thousandSeparator(n, sep)
{
    var sRegExp = new RegExp(\'(-?[0-9]+)([0-9]{3         


        

Answer 1

Here is an ugly script to contrast your beautiful script.

10000000.0001 .toString().split('').reverse().join('')
.replace(/(\d{3}(?!.*\.|$))/g, '$1,').split('').reverse().join('')

Since we don't have lookbehinds, we can cheat by reversing the string and using lookaheads instead.

Here it is again in a more palatable form.

function thousandSeparator(n, sep) {

    function reverse(text) {
        return text.split('').reverse().join('');
    }

    var rx = /(\d{3}(?!.*\.|$))/g;

    if (!sep) {
        sep = ',';
    }

    return reverse(reverse(n.toString()).replace(rx, '$1' + sep));

}