How to traverse Doubly Linked List in JavaScript?

// To traverse and display the list
display() {
    // Check if the List is empty
    if (!this.isEmpty()) {
        // traverse the list using new current pointer
        let curr = this.head;
        console.log("Required list is");

        while (curr !== null) {
            // Display element
            console.log(curr.data);

            // Shift the current pointer
            curr = curr.next;
        }
    }
}

// To display/ traverse list in reverse
displayRev() {
    // Check if the List is empty
    if (!this.isEmpty()) {
        // traverse the list using new current pointer
        let curr = this.tail;
        console.log('Required list in reverse order is')

        while (curr !== null) {
            // Display element
            console.log(curr.data);

            // Shift the current pointer
            curr = curr.prev;
        }
    }
}

// Doubly Linked list Node
class Node {
    // Constructor to create a new node
    // next and prev is by default initialized as null
    constructor(val) {
        // To store the value
        this.data = val;

        // To link the next Node
        this.next = null;

        // TO link the previous Node
        this.prev = null;
    }
}

// Doubly Linked List
class DoublyLinkedList {
    // Constructor to create a new linked list
    constructor() {
        // To contain the first item of the list
        this.head = null;

        // To contain the last item of the list
        this.tail = null;
    }

    // To check if the list is empty
    isEmpty() {
        if (this.head == null) return true;
        return false;
    }

    // Method to add item at the last of doubly linked list
    insertEnd(val) {
        // Create a temporary variable
        let temp = new Node(val);

        // If the list is empty link assign
        // new node to both head and tail
        if (this.head == null) {
            this.head = temp;
            this.tail = temp;
        }

        // else add item to the tail and shift tail
        else {
            temp.prev = this.tail;
            this.tail.next = temp;
            this.tail = this.tail.next;
        }
        console.log('inserted at end',val)

    }

    insertStart(val) {
        // Create a temporary variable
        let temp = new Node(val);

        // If the list is empty link assign
        // new node to both head and tail
        if (this.head == null) {
            this.head = temp;
            this.tail = temp;
        }

        // else add item to the head and shift head backward
        else {
            temp.next = this.head;
            this.head.prev = temp;
            this.head = temp;
        }
        console.log('inserted at start',val)
    }

    // method to insert value at given index
    insertAt(val, pos) {
        // If the index is 0 use insertStart
        // method to insert value as 0 position
        if (pos == 0) return this.insertStart(val);
        let index = pos;
        let curr = this.head;
        // Iterate to the element present
        // just before given index
        while (pos > 1) {
            pos -= 1;
            // If list do not contain enough elements
            if (curr === null)
                return console.log(
                    "Incorrect Position! Index does not exist.",
                    pos,
                    curr.data
                );

            // Shift the poiter at every iteration
            curr = curr.next;
        }

        // After reaching required index create new node
        let temp = new Node(val);

        // Insert node at the required position
        temp.next = curr.next;
        temp.prev = curr;
        curr.next.prev = temp;
        curr.next = temp;
        console.log('inserted at index',index,'value',val)

    }

    // To traverse and display the list
    display() {
        // Check if the List is empty
        if (!this.isEmpty()) {
            // traverse the list using new current pointer
            let curr = this.head;
            console.log('Required list is')

            while (curr !== null) {
                // Display element
                console.log(curr.data);

                // Shift the current pointer
                curr = curr.next;
            }
        }
    }
    displayRev() {
        // Check if the List is empty
        if (!this.isEmpty()) {
            // traverse the list using new current pointer
            let curr = this.tail;
            console.log('Required list in reverse order is')

            while (curr !== null) {
                // Display element
                console.log(curr.data);

                // Shift the current pointer
                curr = curr.prev;
            }
        }
    }
}

// Create new Doubly Linked List
const dll = new DoublyLinkedList();

// Add elements in the list
dll.insertEnd(25);
dll.insertEnd(27);
dll.insertStart(17);
dll.insertStart(29);

dll.insertAt(65,3);

// Display the list
dll.display();
// Display the reverse list
dll.displayRev();