You are given two **non-empty** linked lists representing two non-negative integers. The digits are stored in **reverse order** and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

```
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
```

It should be return a linked list

but this solution `return { val, next: add(l1 && l1.next, l2 && l2.next, newCarry) }`

```
var addTwoNumbers = function(l1, l2) {
return add(l1, l2, 0)
function add(l1, l2, carry) {
const v1 = (l1 && l1.val) || 0
const v2 = (l2 && l2.val) || 0
const sum = v1 + v2 + carry
const newCarry = Math.floor(sum / 10)
const val = sum % 10
return l1 || l2 || carry
? { val, next: add(l1 && l1.next, l2 && l2.next, newCarry) }
: null
}
}
```