LinkedList.js

class Node {

    constructor(value) {
        this.value = value;
        this.previous = null;
        this.next = null;
    }

}

class LinkedList {

    constructor() {
        this.head = null;
        this.tail = null;
    }

    addToHead(value) {

        const newNode = new Node(value);
        const formerHead = this.head;

        this.head = newNode;

        if (formerHead) {
            formerHead.previous = newNode;
            newNode.next = formerHead;
        }

        if (!this.tail) this.tail = newNode;

    }

    addToTail(value) {

        const newNode = new Node(value);
        const formerTail = this.tail;

        this.tail = newNode;

        if (formerTail) {
            formerTail.next = newNode;
            newNode.previous = formerTail;
        }

        if (!this.head) this.head = this.tail;

    }

    removeHead() {

        const removedHead = this.head;

        if (!removedHead) return;

        if (removedHead.next) {
            this.head = removedHead.next;
            this.head.previous = null;
        } else {
            this.head = null;
            this.tail = null;
        }

        return removedHead.value;

    }

    removeTail() {

        const removedTail = this.tail;

        if (!removedTail) return;

        if (removedTail.previous) {
            this.tail = removedTail.previous;
            this.tail.next = null;
        } else {
            this.head = null;
            this.tail = null;
        }

        return removedTail.value;

    }

    search(comparator) {

        let currentNode = this.head;

        if (typeof comparator === 'string') {
            const comparatorString = comparator;
            comparator = function (elementValue) {
                return comparatorString === elementValue;
            }
        }

        while (currentNode !== null) {
            if (comparator(currentNode.value)) return currentNode.value;
            currentNode = currentNode.next;
        }

        return null;

    }

    size() {

        let i = 0;
        let currentNode = this.head;

        while (currentNode !== null) {
            i++;
            currentNode = currentNode.next;
        }

        return i;

    }

}