javascript function kiểm tra mã thẻ tín dụng hợp lệ - validate a valid credit card number

function IsValidCreditCard(ccNumb) {



    ccNumb = ccNumb.ReplaceAll('-', ''); // strip hyphen

    ccNumb = ccNumb.ReplaceAll(' ', '');

    var valid = "0123456789";   // Valid digits in a credit card number

    var len = ccNumb.length;  // The length of the submitted cc number

    var iCCN = parseInt(ccNumb);  // integer of ccNumb

    var sCCN = ccNumb.toString();  // string of ccNumb

    sCCN = sCCN.replace(/^\s+|\s+$/g, '');  // strip spaces

    var iTotal = 0;  // integer total set at zero

    var bNum = true;  // by default assume it is a number

    var bResult = false;  // by default assume it is NOT a valid cc

    var temp;  // temp variable for parsing string

    var calc;  // used for calculation of each digit



    // Determine if the ccNumb is in fact all numbers

    for (var j = 0; j < len; j++) {

        temp = "" + sCCN.substring(j, j + 1);

        if (valid.indexOf(temp) == "-1") { bNum = false; }

    }



    // if it is NOT a number, you can either alert to the fact, or just pass a failure

    if (!bNum) {

        /*alert("Not a Number");*/

        bResult = false;

    }



    // Determine if it is the proper length 

    if ((len == 0) && (bResult)) {  // nothing, field is blank AND passed above # check

        bResult = false;

    } else {  // ccNumb is a number and the proper length - let's see if it is a valid card number

        if (len >= 15) {  // 15 or 16 for Amex or V/MC

            for (var i = len; i > 0; i--) {  // LOOP throught the digits of the card

                calc = parseInt(iCCN) % 10;  // right most digit

                calc = parseInt(calc);  // assure it is an integer

                iTotal += calc;  // running total of the card number as we loop - Do Nothing to first digit

                i--;  // decrement the count - move to the next digit in the card

                iCCN = iCCN / 10;                               // subtracts right most digit from ccNumb

                calc = parseInt(iCCN) % 10;    // NEXT right most digit

                calc = calc * 2;                                 // multiply the digit by two

                // Instead of some screwy method of converting 16 to a string and then parsing 1 and 6 and then adding them to make 7,

                // I use a simple switch statement to change the value of calc2 to 7 if 16 is the multiple.

                switch (calc) {

                    case 10: calc = 1; break;       //5*2=10 & 1+0 = 1

                    case 12: calc = 3; break;       //6*2=12 & 1+2 = 3

                    case 14: calc = 5; break;       //7*2=14 & 1+4 = 5

                    case 16: calc = 7; break;       //8*2=16 & 1+6 = 7

                    case 18: calc = 9; break;       //9*2=18 & 1+8 = 9

                    default: calc = calc;           //4*2= 8 &   8 = 8  -same for all lower numbers

                }

                iCCN = iCCN / 10;  // subtracts right most digit from ccNum

                iTotal += calc;  // running total of the card number as we loop

            }  // END OF LOOP

            if ((iTotal % 10) == 0) {  // check to see if the sum Mod 10 is zero

                bResult = true;  // This IS (or could be) a valid credit card number.

            } else {

                bResult = false;  // This could NOT be a valid credit card number

            }

        }

    }

    return bResult; // Return the results

}