Example of a doubly linked list data structure with ability to append and prepend nodes and traverse to search for a specific value.

doubly_linked_list.js

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

class LinkedList {
  // Set the head and tail to null as there are no nodes currently
  constructor(head, tail) {
    this.head = null,
    this.tail = null
  }

  // traversing through list starting at the head and check if the value exists in the list
  find(value) {
    let currentHead = this.head
    while (currentHead) {
      console.log(currentHead.value)
      if (currentHead.value === value) {
        return currentHead;
      }
      currentHead = currentHead.next;
    }
    return null;
  }

  // Add a new node to the End of the list
  append(value) {
    if (!this.tail) {
      // sets this new node as the head and tail if the list was empty
      this.head = this.tail = new Node(value);
    } else {
      // temporarily set the last node to a variable oldTail
      const oldTail = this.tail;

      // Create a new node
      const newNode = new Node(value);
      
      // Set the new node to be the new tail
      this.tail = newNode

      // point the old tail to the new node to ensure they are linked
      oldTail.next = newNode;

      // Set the previous pointer to point at the oldTail ensuring the link is chained
      this.tail.prev = oldTail
    }
  }

  // add a new node to the Start of the list
  prepend(value) {
    if (!this.head) {
      this.head = this.tail = new Node(value);
    } else {
      const oldHead = this.head;
      this.head = new Node(value)
      this.head.next = oldHead;
      oldHead.prev = this.head;
    }
  }
}
  
  
// Create a new list
const linked1 = new LinkedList

// Add a few nodes to the list
linked1.append(123); 
linked1.append(456);
linked1.append(789);
linked1.prepend(0);

// View the structure of the list
console.log(linked1);

console.log("------------------");

// Search the list for a specified value. returns the node if found otherwise returns null
console.log(linked1.find(45));