Doubly Linked List

class Node {
    constructor(value) {
        this.value = value;
        this.prev = null;
        this.next = null;
    }
}

class DoublyLinkedList {
    constructor(value) {
        this.head = {
            value: value,
            prev: null,
            next: null
        };
        this.tail = this.head;
        this.length = 1;
    }
    
    append(value) {
        const newNode = new Node(value);
        this.tail.next = newNode;
        newNode.prev = this.tail;
        this.tail = newNode;
        this.length++;
        return this;
    }
    
    prepend(value) {
        const newNode = new Node(value);
        newNode.next = this.head;
        this.head.prev = newNode;
        this.head = newNode;
        this.length++;
        return this;
    }
    
    traverseToIndex(index) {
        let counter = 0;
        let currentNode = this.head;
        while (counter !== index) {
            currentNode = currentNode.next;
            counter++;
        }
        return currentNode;
    }
    
    insert(index, value) {
        if (index === 0) {
            return this.prepend(value);
        }
        
        if (index >= this.length) {
            return this.append(value);    
        }
        
        let node = this.traverseToIndex(index - 1);
        
        const newNode = new Node(value);
        const temp = node.next;
        node.next = newNode;
        newNode.prev = node;
        newNode.next = temp;
        temp.prev = newNode;
        this.length++;
        return this;
    }
    
    remove (index) {
        let node = null;
        if (index === 0) {
            node = this.head;
            let temp = node.next;
            temp.prev = null;
            this.head = temp;
            this.length--;
            return this;
        }
        
        node = this.traverseToIndex(index-1);
        let nodeToBeRemoved = node.next;
        let successor = nodeToBeRemoved.next;
        // nodeToBeRemoved.next = null;
        node.next = successor;
        successor.prev = node;
        this.length--;
        return this;
    }
    
    
    // print the elements in the linked list
    printList() {
        const values = [];
        let node = this.head;
        while (node !== null) {
            values.push(node.value);
            node = node.next;
        }
        console.log(values.join(" <=> ") + " length = " + this.length);
    }
}


// -----------------------
const myLinkedList = new DoublyLinkedList(10);
myLinkedList.printList();

myLinkedList.append(5);
myLinkedList.printList();

myLinkedList.append(15);
myLinkedList.printList();

myLinkedList.append(20);
myLinkedList.printList();
// -----------------------
myLinkedList.prepend(1);
myLinkedList.printList();

myLinkedList.prepend(0);
myLinkedList.printList();

myLinkedList.insert(2, 12);
myLinkedList.printList();
myLinkedList.insert(3, 13);
myLinkedList.printList();
myLinkedList.insert(0, 21);
myLinkedList.printList();
myLinkedList.insert(200, 25);
myLinkedList.printList();
// myLinkedList.remove(0);
// myLinkedList.printList();
myLinkedList.remove(3);
myLinkedList.printList();