Add Two Numbers

var addTwoNumbers = function(l1, l2) {
    var sum = l1.val + l2.val,
        l3 = new ListNode(sum % 10),
        node = l3;

    l1 = l1.next;
    l2 = l2.next;
    sum = Math.floor(sum / 10);

    while (l1 || l2 || sum != 0) {
        sum += (l1 ? l1.val : 0) + (l2 ? l2.val : 0);
        node.next = new ListNode(sum % 10);
        node = node.next;
        l1 = l1 ? l1.next : null;
        l2 = l2 ? l2.next : null;
        sum = Math.floor(sum / 10);
    }

    return l3;
};