Doubly Linked List

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

class DoublyLinkedList {
    constructor() {
        this.length = 0;
        this.head = null;
        this.tail = null;
    }

    // Add node to the start of the list
    insertHead(value) {
        const newNode = new Node(value);
        if (this.length === 0) {
            this.head = newNode;
            this.tail = newNode;
        } else {
            this.head.prev = newNode;
            newNode.next = this.head;
            this.head = newNode;
        }
        this.length++;
        return newNode;
    }

    // Add node to the end of the list
    insertTail(value) {
        const newNode = new Node(value);
        if (this.length === 0) {
            this.head = newNode;
            this.tail = newNode;
        } else {
            this.tail.next = newNode;
            newNode.prev = this.tail;
            this.tail = newNode;
        }
        this.length++;
        return newNode;
    }

    // Remove node at the start of the list.
    removeHead() {
        if (this.length === 0) {
            return null;
        }

        const nodeToRemove = this.head;

        if (this.length === 1) {
            this.head = null;
            this.tail = null;
        } else {
            this.head = nodeToRemove.next;
            this.head.prev = null;
            nodeToRemove.next = null;
        }
        this.length--;
        return nodeToRemove.value;
    }

    // Remove node at the end of the list.
    removeTail() {
        if (this.length === 0) {
            return null;
        }

        const nodeToRemove = this.tail;

        if (this.length === 1) {
            this.head = null;
            this.tail = null;
        } else {
            this.tail = nodeToRemove.prev;
            this.tail.next = null;
            nodeToRemove.prev = null;
        }
        this.length--;
        return nodeToRemove.value;
    }

    getHead() {
        return this.head ? this.head.value : null;
    }

    getTail() {
        return this.tail ? this.tail.value : null;
    }

    size() {
        return this.length;
    }

    // Return list values
    toString() {
        const list = [];
        let currentNode = this.head;
        while (currentNode !== null) {
            list.push(JSON.stringify(currentNode.value));
            currentNode = currentNode.next;
        }
        return list.toString();
    }
}

const dll = new DoublyLinkedList();

Operation	Time Complexity
insertHead	O(1)
insertTail	O(1)
removeHead	O(1)
removeTail	O(1)
getHead	O(1)
getTail	O(1)
size	O(1)
toString	O(n)

Data Structures for Coding Interviews in JavaScript - Learn InteractivelyEducative: Interactive Courses for Software Developers