A linked list created in JavaScript.

linked-list.js

//
// This is only a SKELETON file for the 'Linked List' exercise. It's been provided as a
// convenience to get you started writing code faster.
//

/// Supposing that the list has at least one item.
class Node {
  constructor(value, previous, next) {
    this.value = value;
    this.previous = previous;
    this.next = next;
  }
}
// export
export class LinkedList {
  constructor() {
    this._sentinel = new Node(0, null, null);
    this._sentinel.next = this._sentinel;
    this._sentinel.previous = this._sentinel;
    this.itemsNum = 0;
  }
  // Inserts value at back
  push(value) {
    let lastItem;
    if (this._sentinel.previous != null) {
      lastItem = this._sentinel.previous;
      lastItem.next = new Node(value, lastItem, null);
      lastItem = lastItem.next;
    } else {
      lastItem = new Node(value, this._sentinel, this._sentinel);
      this._sentinel.next = lastItem;
    }

    // while (lastItem.next != null) {
    //   lastItem = lastItem.next;
    // }
    this._sentinel.previous = lastItem;
    lastItem.next = this._sentinel;
    this.itemsNum++;
  }

  // Removes value from the back
  pop() {
    let lastItem = this._sentinel.previous;

    // while (lastItem.next != null) {
    //   lastItem = lastItem.next;
    // }
    this._sentinel.previous = lastItem.previous;
    let value = lastItem.value;
    lastItem = null;
    this.itemsNum--;
    return value;
  }

  // Removes value at front
  shift() {
    let frontItem;
    frontItem = this._sentinel.next;
    let value = frontItem.value;
    frontItem.next.previous = this._sentinel;
    this._sentinel.next = frontItem.next;
    this.itemsNum--;
    return value;
  }
  // Inserts value at front
  unshift(value) {
    let frontItem;
    frontItem = this._sentinel.next;
    this._sentinel.next = new Node(value, this._sentinel, frontItem);
    frontItem.previous = this._sentinel.next;
    this.itemsNum++;
  }
  // Deletes specific element.
  delete(value) {
    let currentItem = this._sentinel.next;
    while (currentItem != this._sentinel) {
      if (currentItem.value == value) {
        let previousItem = currentItem.previous;
        let nextItem = currentItem.next;
        previousItem.next = nextItem;
        nextItem.previous = previousItem;
        this.itemsNum--;

        break;
      } else {
        currentItem = currentItem.next;
      }
    }
  }
  count() {
    return this.itemsNum;
  }
}

var list = new LinkedList();
list.push(5);
list.push(4);
list.push(3);
list.push(2);

list.delete(2);
console.log(list.pop());

console.log(list.pop());
console.log(list.pop());