Doubly linked lists

The difference between a doubly linked list and a normal or singly linked list is that in a linked list we make the link from one node to the next one only, while in a doubly linked list, we have a double link: one for the next element and one for the previous element, as shown in the following diagram:

Doubly linked list with previous and next nodes

Let's get started with the changes that are needed to implement the DoublyLinkedList class. We will start by declaring the node of our doubly linked list:

class DoublyLinkedListNode {
  constructor(data, next = null, previous = null) {
    this.data = data;
    this.next = next;
    this.previous = previous; // new
  } 
}

In a doubly linked list, each node maintains two references:

1. next: a pointer to the next node in the list.
2. previous: a pointer to the previous node in the list.

This dual linking enables efficient traversal in both directions. To accommodate this structure, we add the previous pointer to our...