Merge sort

const mergeSortedLists = (h1, h2) => {
    let head;
    let temp;

    if (!h1)
        return h2;

    if (!h2)
        return h1;

    while (h1 || h2) {
        if (!h2) {
            temp.next = new ListNode(h1.value, null);
            temp = temp.next;
            h1 = h1.next;

        } else if (!h1) {
            temp.next = new ListNode(h2.value, null);
            temp = temp.next;
            h2 = h2.next;

        } else if (!head && h1.value >= h2.value) {
            head = new ListNode(h2.value, null);
            temp = head;
            h2 = h2.next;

        } else if (head && h1.value >= h2.value) {
            temp.next = new ListNode(h2.value, null);
            temp = temp.next
            h2 = h2.next;

        } else if (!head && h1.value <= h2.value) {
            head = new ListNode(h1.value, null);
            temp = head;
            h1 = h1.next;

        } else if (head && h1.value <= h2.value) {
            temp.next = new ListNode(h1.value, null);
            temp = temp.next
            h1 = h1.next;
        }
    }

    return head;
}