How can I check for the correct location of commas in a number entered by a user?

Question

I'm looking for a good way to check a number that a user has entered for correct position of an optional comma(s).

For example

1,000,000.00 = correct
1000000 = correct
1,00,000.00 = incorrect
,100,000 = incorrect

So it looks like i need to check to see that there is at least one number to the left and 3 numbers to the right of the comma. Or is there a regex way to do this?

Answer 1

/^(?:\d+|\d{1,3}(?:,\d{3})*)(?:\.\d+)?$/

Answer 2

What are you going to use this for? Or put another way, why care? Why not just strip out all commas and convert it to a numeric type?

Answer 3

Check out this website: http://blog.stevenlevithan.com/archives/commafy-numbers

Here's the code snippet:

String.prototype.commafy = function () {
    return this.replace(/(^|[^\w.])(\d{4,})/g, function($0, $1, $2) {
     return $1 + $2.replace(/\d(?=(?:\d\d\d)+(?!\d))/g, "$&,");
    });
}

Number.prototype.commafy = function () {
    return String(this).commafy();
}

What you can do is replace all commas and then use this code to add in the commas yourself.

Hope that helps.