[Javascript] leetcode784:Odd Even Linked List

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/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */

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

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
const oddEvenList = function(head) {
  if (!head) return null;
  let odd = head;
  let even = head.next;
  let evenHead = even;

  while (even !== null && even.next !== null) {
    odd.next = even.next;
    odd = odd.next;
    even.next = odd.next;
    even = even.next;
  }

  odd.next = evenHead;

  return head;
};