Add two numbers (LeetCode #2)

add_two_numbers.js

function ListNode(val, next) {
    this.val = (val === undefined ? 0 : val);
    this.next = (next === undefined ? null : next);
}

const addTwoNumbers = (l1, l2) => {
    let carry = 0;
    let result = new ListNode(-1)
    let dummy = result;

    while (l1 || l2 || carry) {
        let l1Val = l1 ? l1.val : 0;
        let l2Val = l2 ? l2.val : 0;

        let nextDigit = (l1Val + l2Val + carry) % 10;
        result.next = new ListNode(nextDigit)
        result = result.next;
        carry = Math.floor((l1Val + l2Val + carry) / 10);
        l1 = l1 ? l1.next : null;
        l2 = l2 ? l2.next : null;
    }

    return dummy.next;
}

let listNode0 = new ListNode(3)
let listNode1 = new ListNode(4, listNode0)
let listNode2 = new ListNode(2, listNode1)

let listNode01 = new ListNode(4)
let listNode11 = new ListNode(6, listNode01)
let listNode21 = new ListNode(5, listNode11)

let ResultListNode = addTwoNumbers(listNode2, listNode21);
let result = [];
while (ResultListNode.next) {
    result.push(ResultListNode.val);
    ResultListNode = ResultListNode.next;
    if (ResultListNode.next === null) {
        result.push(ResultListNode.val);
    }
}

console.assert(result, [7,0,8]);