Javascript to validate HKID number

function IsHKID(str) {

var strValidChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

// basic check length

if (str.length < 8)

return false;

// handling bracket

if (str.charAt(str.length-3) == '(' && str.charAt(str.length-1) == ')')

str = str.substring(0, str.length - 3) + str.charAt(str.length -2);

// convert to upper case

str = str.toUpperCase();

// regular expression to check pattern and split

var hkidPat = /^([A-Z]{1,2})([0-9]{6})([A0-9])$/;

var matchArray = str.match(hkidPat);

// not match, return false

if (matchArray == null)

return false;

// the character part, numeric part and check digit part

var charPart = matchArray[1];

var numPart = matchArray[2];

var checkDigit = matchArray[3];

// calculate the checksum for character part

var checkSum = 0;

if (charPart.length == 2) {

checkSum += 9 * (10 + strValidChars.indexOf(charPart.charAt(0)));

checkSum += 8 * (10 + strValidChars.indexOf(charPart.charAt(1)));

} else {

checkSum += 9 * 36;

checkSum += 8 * (10 + strValidChars.indexOf(charPart));

}

// calculate the checksum for numeric part

for (var i = 0, j = 7; i < numPart.length; i++, j--)

checkSum += j * numPart.charAt(i);

// verify the check digit

var remaining = checkSum % 11;

var verify = remaining == 0 ? 0 : 11 - remaining;

return verify == checkDigit || (verify == 10 && checkDigit == 'A');

}