Credit Card Validation : Validation « Form Control « JavaScript DHTML

Credit Card Validation


/*
JavaScript Unleashed, Third Edition
by Richard Wagner and R. Allen Wyke 

ISBN: 067231763X
Publisher Sams CopyRight 2000

*/
<html>
<head>
<title>Credit Card Validation</title>
<script language="JavaScript">
<!--begin script
function isCreditCard(textObj) {
 /*
  *  This function validates a credit card entry.
  *  If the checksum is ok, the function returns true.
  */
   var ccNum;
   var odd = 1;
   var even = 2;
   var calcCard = 0;
   var calcs = 0;
   var ccNum2 = "";
   var aChar = '';
   var cc;
   var r;
   
   ccNum = textObj.value;
   for(var i = 0; i != ccNum.length; i++) {
      aChar = ccNum.substring(i,i+1);
      if(aChar == '-') {
         continue;
      }

      ccNum2 = ccNum2 + aChar;
   }
   
   cc = parseInt(ccNum2);
   if(cc == 0) {
      return false;
   }
   r = ccNum.length / 2;
   if(ccNum.length - (parseInt(r)*2) == 0) {
      odd = 2;
      even = 1;
   }
   
   for(var x = ccNum.length - 1; x > 0; x--) {
      r = x / 2;
      if(r < 1) {
         r++;
      }
      if(x - (parseInt(r) * 2) != 0) {
         calcs = (parseInt(ccNum.charAt(x - 1))) * odd;
      }
      else {
         calcs = (parseInt(ccNum.charAt(x - 1))) * even;
      }
      if(calcs >= 10) {
         calcs = calcs - 10 + 1;
      }
      calcCard = calcCard + calcs;
   }
   
   calcs = 10 - (calcCard % 10);
   if(calcs == 10) {
      calcs = 0;
   }
   
   if(calcs == (parseInt(ccNum.charAt(ccNum.length - 1)))) {
      return true;
   }
   else {
      return false;
   }
}

// end script-->
</script>
</head>
   
<BODY>
<h1>Credit Card Validation</h1>
<form name="form1">
<input type="text"
   size=16
   maxlength=16
   name="data">
<input type="button"
   name="CheckButton"
   value="Validate"
   onClick="document.form1.result.value = '' +
    isCreditCard(document.form1.data)">
<br>
Result <input type="text"
   size=16
   maxlength=16
   name="result">
</form>
</body>
</html>

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