카드 플래그를 반환하는 Javascript 방법입니다.

by default, the flag returned is 'visa' if nothings match.

   returnflag('2014 7722409 8894');

   function returnflag(cardNumber) {
        cardNumber = cardNumber.toString().replace(/[^0-9]+/g, '');
        const cards = {
            visa: /^4[0-9]{12}(?:[0-9]{3})?/,
            mastercard: /^(((51)|(52)|(53)|(54)|(55))\d{0,14})/,
            diners: /^3(?:0[0-5]|[68][0-9])[0-9]{11}/,
            amex: /^3[47][0-9]{13}/,
            discover: /^6(?:011|5[0-9]{2})[0-9]{12}/,
            hipercard: /^(606282\d{10}(\d{3})?)|(3841\d{15})/,
            elo: /^((((636368)|(438935)|(504175)|(451416)|(636297))\d{0,10})|((5090)|(5067)|(4576)|(4011))\d{0,12})/,
            jcb: /^(?:2131|1800|35\d{3})\d{11}/,
            aura: /^(5078\d{2})(\d{2})(\d{11})$/
        };

        for (let flag in cards) {
            if (cards[flag].test(cardNumber)) {
                return flag;
            }
        }
        return 'visa';
    }