Quick and dirty code to insert commas after every 3 digits (also handles decimals correctly)

DirtyCommas.js

// via @DmitryBaranovsk
function dirtyCommas(num) {
    return String(num).replace(/^\d+(?=\.|$)/, function (int) { return int.replace(/(?=(?:\d{3})+$)(?!^)/g, ","); });
}

Ya but still has a problem with the long decimal values.... I think a solution is close :D

@jdalton I think it even further now. Anyway I give up to solve it with one regexp. :)
Current solution is “good enough”.

ok so the thing I could come up with is:

String(value).replace(/(\.\d+)|(?=(?:\d{3})+\b)(?!\b)/g, function(m, $1) { return $1 || ',' });

It requires passing a function but still just 1 regexp.

I just applied jdalton's 2011.03.04 version to something I'm working on and found that I'll need a way to make it skip over dates. Example confusion: "...vol. 1, no. 4, pp. 4-9, July/August 1,995, concluded that..." (should contain "August 1995", rather than implying the nonsensical "July through August 1st, 995"). Guess I have my work cut out for me.

I've been trying several versions of this and it works great with numbers that are not thousand rounded.
for instance, 1234 goes 1,234.00.
But when I have 4000, I get a 4,0.00, so it basically removes 3 zeros off the thousands portion.
Does anyone have a clue?