JavaScript RegEx format string containing American Express card number

Question

I'm trying to format a string containing an American Express credit card number using a regular expression. Here's what I'm using for Visa, MasterCard and Discover number formatting, but it obviously doesn't work for American Express:

var formatVisaMasterCardDiscover = function (
    number) {
    return number.split(/(?=(?:\d{4})+($))/).filter(function (
        n) {
        return (n != "");
    }).join("-");
};

So, I'm curious what the regular expression for an Amex number would be. The format should {4}-{6}-{5}. I'd appreciate any help because I couldn't find anything while searching except about how to validate it which is not what I want. I want to format it.

Answer 1

You can use:

var ccNum = '341256789012345';

var ccFmt = ccNum.replace(/\b(\d{4})(\d{6})(\d{5})\b/, '$1-$2-$3');
//=> 3412-567890-12345

RegEx Demo