1. /**
    2.  * Definition for singly-linked list.
    3.  * function ListNode(val, next) {
    4.  *     this.val = (val===undefined ? 0 : val)
    5.  *     this.next = (next===undefined ? null : next)
    6.  * }
    7.  */
    8. /**
    9.  * @param {ListNode} head
    10.  * @return {ListNode}
    11.  */
    12. var middleNode = function(head) {
    13.    let list = [],
    14.           node = head
    16.    while(node) {
    17.      list.push(node)
    18.      node = node.next
    19.    }
    21.    return list[Math.floor(list.length / 2)]
    22. };