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

Someone mentioned that lookbehind isn't possible in Javascript RegExp. Here is a great page that explains how to use lookaround (lookahead and lookbehind).

http://www.regular-expressions.info/lookaround.html