Javascript Program for Rotate Doubly linked list by N nodes

// javascript program to rotate a Doubly linked 
// list counter clock wise by N times 

/* Link list node */
class Node {
    constructor() {
        this.data = 0;
        this.prev = null;
        this.next = null;
    }
}
let head = null;

// This function rotates a doubly linked
// list counter-clockwise and updates the
// head. The function assumes that N is
// smallerthan size of linked list. It
// doesn't modify the list if N is greater
// than or equal to size
function rotate(N) {
    if (N == 0)
        return;

    // Let us understand the below code
    // for example N = 2 and
    // list = a <-> b <-> c <-> d <-> e.
    let current = head;

    // current will either point to Nth
    // or NULL after this loop. Current
    // will point to node 'b' in the
    // above example
    let count = 1;
    while (count < N && current != null) {
        current = current.next;
        count++;
    }

    // If current is NULL, N is greater
    // than or equal to count of nodes
    // in linked list. Don't change the
    // list in this case
    if (current == null)
        return;

    // current points to Nth node. Store
    // it in a letiable. NthNode points to
    // node 'b' in the above example
    let NthNode = current;

    // current will point to last node
    // after this loop current will point
    // to node 'e' in the above example
    while (current.next != null)
        current = current.next;

    // Change next of last node to previous
    // head. Next of 'e' is now changed to
    // node 'a'
    current.next = head;

    // Change prev of Head node to current
    // Prev of 'a' is now changed to node 'e'
    (head).prev = current;

    // Change head to (N+1)th node
    // head is now changed to node 'c'
    head = NthNode.next;

    // Change prev of New Head node to NULL
    // Because Prev of Head Node in Doubly
    // linked list is NULL
    (head).prev = null;

    // change next of Nth node to NULL
    // next of 'b' is now NULL
    NthNode.next = null;
}

// Function to insert a node at the
// beginning of the Doubly Linked List
function push(new_data) {
    let new_node = new Node();
    new_node.data = new_data;
    new_node.prev = null;
    new_node.next = (head);
    if ((head) != null)
        (head).prev = new_node;
    head = new_node;
}

/* Function to print linked list */
function printList(node) {
    let output = '';
    while (node != null && node.next != null) {
        output += node.data + " ";
        node = node.next;
    }
    if (node != null)
        output += node.data
    console.log(output);

}

// Driver's Code

/* Start with the empty list */
// Node head = null;

/*
 * Let us create the doubly linked list a<->b<->c<->d<->e
 */
push('e');
push('d');
push('c');
push('b');
push('a');

let N = 2;

console.log("Given linked list:");
printList(head);
rotate(N);
console.log();
console.log("Rotated Linked list: ");
printList(head);