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# statement

}
bIsOdd = !bIsOdd;
}
}
else
statement to
if (bIsOdd)
accomplishes adding the odd position digits together. If the
number is greater than 9 (which means it has two digits), the number is transformed using a variety of
methods talked about earlier in the book:
1.
The number is transformed into a string using
toString()
.
2.
The string is then split into an array of two characters using
split()
. For example, 12 would be
split into an array of
“1”
and
“2”
.
3.
The array is combined with a plus sign using
join()
, so
“1”
and
“2”
become
“1+2”
.
4.
The resulting string is then passed in to
eval()
, which interprets it as literal code (so
“1+2”
is
added as 1+2 and returns 3).
The very last step is to add the two sums (from the even and odd position digits) and perform a modu-
lus (remainder) operation on the result. If the number is valid, the sum is equally divisible by 10 (so it
will be equal to 20, 30, 40, and so on).
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);
}
Add this method back into the
isValidMasterCard()
method, and you’re done:
function isValidMasterCard(sText) {
var reMasterCard = /^(5[1-5]\d{2})[\s\-]?(\d{4})[\s\-]?(\d{4})[\s\-]?(\d{4})\$/;
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Chapter 7
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