isMastercard

isMastercard :: a → Boolean

Reports whether the received value is a valid credit card number and is a Mastercard card

import isMastercard from 'deep-waters/credit-cards/isMastercard';

isMastercard(5276023546902691); // Mastercard → true

isMastercard(4286124395547263); // VISA → false
isMastercard(6011583945260254); // Discover → false
isMastercard(38716394960899); // Diners Club → false
isMastercard(3528701379615495); // JCB → false
isMastercard('6011-5839-4526-0254'); // Credit card format → false
isMastercard("foo"); // → false
isMastercard(undefined); // → false

Please note, isMastercard assumes the receiving value is a number or a string without the usual dashes. It only evaluates the credit card number, not its format.