```
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} l1
* @param {ListNode} l2
* @return {ListNode}
*/
var addTwoNumbers = function(l1, l2) {
var List = new ListNode(0);
var head = List;
var sum = 0;
var carry = 0;
while(l1!==null||l2!==null||sum>0){
if(l1!==null){
sum = sum + l1.val;
l1 = l1.next;
}
if(l2!==null){
sum = sum + l2.val;
l2 = l2.next;
}
if(sum>=10){
carry = 1;
sum = sum - 10;
}
head.next = new ListNode(sum);
head = head.next;
sum = carry;
carry = 0;
}
return List.next;
};
```