Function that checks if a swedish personnummer is valid

personnummer.js

/*
 * Function that checks if a swedish personnummer is valid.
 * Author: André Laszlo <andre@laszlo.nu>
 */

function check_personnummer(pnr) {
	// Do formatting and sanity control
	pnr = pnr.replace(/[^0-9]/g, ''); // only keep digits
	if (12 == pnr.length) // year format 1985 → 85
		pnr = pnr.substr(2);
	if (10 != pnr.length) // check length
		return false;
	if (pnr.substr(2,2) > 12) // check month
		return false;
	if (pnr.substr(4,2) > 31 || pnr.substr(4,2) == 0) // check date
		return false;
	var parts = pnr.split('').map(function(i){
		return Number(i);
	});
	// Then run the mod 10 algorithm to produce check digit
	var control = parts.pop();
	var inc = 0, multiplicator = 2, product;
	for (var i in parts) {
		product = parts[i] * multiplicator;
		if (product > 9)
			inc += product - 9;
		else
			inc += product;
		multiplicator = multiplicator == 1 ? 2 : 1;
	}
	var control_ = 10 - (inc - Math.floor(inc/10)*10);
	if (10 == control_)
		control_ = 0;
	return control == control_;
}

// define test data
var tests = [{test: '19850811-1237', expected: true},
			 {test: '19850811-1234', expected: false},
			 {test: '8508111237', expected: true},
			 {test: '8508111234', expected: false},
			 {test: '198508111237', expected: true},
			 {test: '198508111234', expected: false},
			 {test: '8702141238', expected: true},
			 {test: '8702141234', expected: false},
			 {test: '19860930-1232', expected: true},
			 {test: '19860930-1234', expected: false},
			 {test: 'abc', expected: false},
			 {test: '', expected: false},
			 {test: '123', expected: false},
			 {test: '1234567890', expected: false},
			 {test: '9999999999', expected: false},
			 {test: '0000000000', expected: false},
			]

// run tests
var result, expected, count = 0, fail = 0;
for (var i in tests) {
	count++;
	result = check_personnummer(tests[i].test);
	if (result != tests[i].expected) {
		fail++;
		print(tests[i].test +
			  " : Returned value " +
			  result.toString() +
			  " does not equal expected value " +
			  tests[i].expected.toString());
	}
}
print(count + " tests completed, " + fail + " failed");

http://www.skatteverket.se/folkbokforing/ovrigt/personnummer.4.18e1b10334ebe8bc80001502.html