Credit Card Number Validation

Determine if a credit card number could be valid before submitting it for real-time online authentication. Based on ANSI X4.13, the LUHN formula, aka the Mod 10 algorithm is used to validate accurate credit card numbers. Heavily commented.

Sample:

Credit Card Number:

Insert this code before </head> <script type="text/javascript"> <!-- /* This script and many more are available free online at The JavaScript Source!! http://javascript.internet.com Created by: David Leppek :: https://www.azcode.com/Mod10 Basically, the alorithum takes each digit, from right to left and muliplies each second digit by two. If the multiple is two-digits long (i.e.: 6 * 2 = 12) the two digits of the multiple are then added together for a new number (1 + 2 = 3). You then add up the string of numbers, both unaltered and new values and get a total sum. This sum is then divided by 10 and the remainder should be zero if it is a valid credit card. Hense the name Mod 10 or Modulus 10. */ function Mod10(ccNumb) { // v2.0 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 } } } // change alert to on-page display or other indication as needed. if(bResult) { alert("This IS a valid Credit Card Number!"); } if(!bResult){ alert("This is NOT a valid Credit Card Number!"); } return bResult; // Return the results } // --> </script>

Insert this code before </body> <form name="Form1"> <table width="50%" border="0" cellspacing="0" cellpadding="5"> <tr> <td width="50%" align="right">Credit Card Number: </td> <td width="50%"> <input name="CreditCard" type="text" value="4012888888881881" size="18" maxlength="16" style="border: 1px solid #000098; padding: 3px;"> </td> </tr> <tr> <td colspan="2" align="center"> <input type="button" name="Button" style="color: #fff; background: #000098; font-weight:bold; border: solid 1px #000;" value="TEST CARD NUMBER" onClick="return Mod10(document.Form1.CreditCard.value);"> </td> </tr> </table> </form>