A Javascript implementation of a Doubly-Linked List.

DoublyLinkedList.js

function Node(value) {
  this.data = value;
  this.previous = null;
  this.next = null;
}

function DoublyList() {
  this._length = 0;
  this.head = null;
  this.tail = null;
}

DoublyList.prototype.add = function(data) {
  let node = new Node(data);
  if (this._length) {
    this.tail.next = node;
    node.previous = this.tail;
    this.tail = node;
  } else {
    this.head = node;
    this.tail = node;
  }
  this._length += 1;
  return node;
};

DoublyList.prototype.searchNodeAt = function(position) {
  let currentNode = this.head,
      length = this._length,
      count = 1;
  
  if (length === 0 || position < 1 || position > length) {
    throw new Error("Non-existant node in this list");
  }
  
  while (count < position) {
    currentNode = currentNode.next;
    count += 1;
  }
  
  return currentNode;
};

DoublyList.prototype.remove = function(position) {
  let currentNode = this.head,
      length = this._length,
      count = 1,
      beforeNodeToDelete = null,
      nodeToDelete = null,
      deletedNode = null,
      afterNodeToDelete = null;
  
  if (length === 0 || position > length || position < 1) {
    throw new Error("Non-existant node in this list"); 
  }
  
  if (position === 1) {
    this.head = currentNode.next;
    
    if (!this.head) {
      this.head.previous = null;
    } else {
      this.tail = null;
    }
  } else if (position === this._length) {
    this.tail = this.tail.previous;
    this.tail.next = null;
  } 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 -= 1;
  return "Node was removed";
};