Why does head change in this Linked List? - linked-list

Question

Why does the head change here?
I thought assigning oddPointer to head would allow me to traverse through the list without changing head. This does not seem to be the case. When I log(head) it appears as 1->3->5, why is it not 1->2->3->4->5?
Is there a way to complete this without changing head?
// JavaScript
var oddEvenList = function (head) {
let oddList = new ListNode(-1);
let oddCopy = oddList;
let cnt = 0;
let oddPointer = head;
while (oddPointer) {
cnt++;
if (cnt % 2 !== 0) {
oddList.next = oddPointer; // -1,1,3,5
oddList = oddList.next;
}
oddPointer = oddPointer.next;
}
console.log(oddList);
console.log(oddCopy);
console.log(head);
console.log(oddPointer);
return -1;
}
function ListNode(val, next) {
this.val = (val === undefined ? 0 : val)
this.next = (next === undefined ? null : next)
}
let a1 = new ListNode(1);
let a2 = new ListNode(2);
let a3 = new ListNode(3);
let a4 = new ListNode(4);
let a5 = new ListNode(5)
a1.next = a2;
a2.next = a3;
a3.next = a4;
a4.next = a5;
console.log(oddEvenList(a1));