ES6 Doubly Linked List

doubly-linked-list.js

class Node {
  constructor (value) {
    this.data = value
    this.previous = null
    this.next = null
  }
}
 
class DoublyList {
  constructor() {
    this._length = 0
    this.head = null
    this.tail = null
  }
 
  add(value) {
    const node = new Node(value)
 
    if (this._length) {
        this.tail.next = node
        node.previous = this.tail
        this.tail = node
    } else {
        this.head = node
        this.tail = node
    }
 
    this._length++
 
    return node
  }
 
  searchNodeAt(position) {
    let currentNode = this.head
    let length = this._length
    let count = 1
    const message = {failure: 'Failure: non-existent node in this list.'}
 
    // 1st use-case: an invalid position
    if (length === 0 || position < 1 || position > length) {
        throw new Error(message.failure)
    }
 
    // 2nd use-case: a valid position
    while (count < position) {
      currentNode = currentNode.next
      count++
    }
 
    return currentNode
  }
 
  remove(position) {
    let currentNode = this.head
    let length = this._length
    let count = 1
    const message = {failure: 'Failure: non-existent node in this list.'}
    let beforeNodeToDelete = null
    let nodeToDelete = null
    let deletedNode = null
 
    // 1st use-case: an invalid position
    if (length === 0 || position < 1 || position > length) {
      throw new Error(message.failure)
    }
    // 2nd use-case: the first node is removed
    if (position === 1) {
      this.head = currentNode.next;
      // 2nd use-case: there is a second node
      if (!this.head) {
        this.head.previous = null
      // 2nd use-case: there is no second node
      } else {
        this.tail = null
      }
    // 3rd use-case: the last node is removed
    } else if (position === this._length) {
      this.tail = this.tail.previous
      this.tail.next = null
    // 4th use-case: a middle node is removed
    } else {
      while (count < position) {
        currentNode = currentNode.next
        count++
      }
      beforeNodeToDelete = currentNode.previous
      nodeToDelete = currentNode
      afterNodeToDelete = currentNode.next

      beforeNodeToDelete.next = afterNodeToDelete
      afterNodeToDelete.previous = beforeNodeToDelete
      deletedNode = nodeToDelete
      nodeToDelete = null
    }
 
    this._length--
    
    return message.success
  }
}

export default DoublyList

Original code for article can be found here: https://code.tutsplus.com/articles/data-structures-with-javascript-singly-linked-list-and-doubly-linked-list--cms-23392