Credit Card CheckSum Javascript

CreditCardCheckSum.js

function checksumCC(creditCardString){
	sum = creditCardString
		.split('')
		.reverse()
		.reduce(function(total, num, i){
			num = parseInt(num, 10);
			if(i%2 !== 0){
				num *= 2;
				if(num>9){
					num -= 9;
				}
			}
			return total + num;
		}, 0);
	return (sum%10 === 0);
}