Odd Even Linked List LeetCode solution in JavaScript

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/**
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 * Definition for singly-linked list.
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 * function ListNode(val, next) {
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 *     this.val = (val===undefined ? 0 : val)
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 *     this.next = (next===undefined ? null : next)
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 * }
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 */
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/**
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 * @param {ListNode} head
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 * @return {ListNode}
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 */
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var oddEvenList = function (head) {
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  if (!head || !head.next) return head;
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  let odd = head,
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    even = head.next,
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    firstEven = even;
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  while (even && even.next) {
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    odd.next = even.next;
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    odd = odd.next;
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    even.next = odd.next;
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    even = even.next;
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  }
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  odd.next = firstEven;
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  return head;
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};