Add Two Numbers

 1 var addTwoNumbers = function(l1, l2) {
 2     var sum = l1.val + l2.val,
 3         l3 = new ListNode(sum % 10),
 4         node = l3;
 5 
 6     l1 = l1.next;
 7     l2 = l2.next;
 8     sum = Math.floor(sum / 10);
 9 
10     while (l1 || l2 || sum != 0) {
11         sum += (l1 ? l1.val : 0) + (l2 ? l2.val : 0);
12         node.next = new ListNode(sum % 10);
13         node = node.next;
14         l1 = l1 ? l1.next : null;
15         l2 = l2 ? l2.next : null;
16         sum = Math.floor(sum / 10);
17     }
18 
19     return l3;
20 };