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 optional commas.

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

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 2

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

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.

Answer 4

Here’s a pattern that answers your question. There are also many other number-related patterns there, including ones that are maintainable — something no one ever seems to worry about.