Javascript function to determine a credit card type by its number.

verifyCardType.js

        //This function makes use of the getDigitAt() method which is found in a gist here: https://gist.github.com/ryanhamley/73140d5e9710a9a71fa0
        function verifyCardType (_num) {
          //cast primitive number _num to a Number object to allow for using the getDigitAt() method
          var num = Number(_num);

          if (num.getDigitAt(0) === 4) {
            return 'Visa';
          }

          switch (num.getDigitAt(0, 2)) {
            case 34:
            case 37:
              return 'American Express';
            case 35:
              return 'JCB';
            case 36:
            case 38:
              return 'Diner\'s Club';
            case 51:
            case 52:
            case 53:
            case 54:
            case 55:
              return 'MasterCard';
            case 65:
              return 'Discover';
          }

          switch (num.getDigitAt(0, 3)) {
            case 300:
            case 301:
            case 302:
            case 303:
            case 304:
            case 305:
              return 'Diner\'s Club';
          }

          switch (num.getDigitAt(0, 4)) {
            case 2131:
            case 1800:
              return 'JCB';
            case 6011:
              return 'Discover';
          }

          //if none of the above, return 'Unknown';
          return 'Unknown';
        }