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<HTML>
<head>
<title>Visa Example</title>
<script type="text/javascript">
function luhnCheckSum(sCardNum) {
var iOddSum = 0;
var iEvenSum = 0;
var bIsOdd = true;
for (var i=sCardNum.length-1; i >= 0; i--) {
var iNum = parseInt(sCardNum.charAt(i));
if (bIsOdd) {
iOddSum += iNum;
} else {
iNum = iNum * 2;
if (iNum > 9) {
iNum = eval(iNum.toString().split("").join("+"));
}
iEvenSum += iNum;
}
bIsOdd = !bIsOdd;
}
return ((iEvenSum + iOddSum) % 10 == 0);
}
function isValidVisa(sText) {
var reVisa = /^(4\d{12}(?:\d{3})?)$/;
if (reVisa.test(sText)) {
return luhnCheckSum(RegExp.$1);
} else {
return false;
}
}
function validate() {
var oInput1 = document.getElementById("txt1");
if (isValidVisa(oInput1.value)) {
alert("Valid");
} else {
alert("Invalid!");
}
}
</script>
</head>
<body>
<P>Visa Number: <input type="text" id="txt1" /><br />
<input type="button" value="Validate" onclick="validate()" /></p>
</body>
</html>
Quote from:
Professional JavaScript for Web Developers
by Nicholas C. Zakas (Author)
# Paperback: 672 pages
# Publisher: Wrox (April 22, 2005)
# Language: English
# ISBN-10: 0764579088
# ISBN-13: 978-0764579080
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