Regular Expression for formatting numbers in JavaScript

Question

I need to display a formatted number on a web page using JavaScript. I want to format it so that there are commas in the right places. How would I do this with a regular exp

Answer 1

Try something like this:

function add_commas(numStr)
{
    numStr += '';
    var x = numStr.split('.');
    var x1 = x[0];
    var x2 = x.length > 1 ? '.' + x[1] : '';
    var rgx = /(\d+)(\d{3})/;
    while (rgx.test(x1)) {
        x1 = x1.replace(rgx, '$1' + ',' + '$2');
    }
    return x1 + x2;
}

Answer 2

I think you would necessarily have to do multiple passes to achieve this with regular expressions. Try the following:

1. Run a regex for one digit followed by 3 digits.
2. If that regex matches, replace it with the first digit, then a comma, then the next 3 digits.
3. Repeat until (1) finds no matches.