LinkedList created by aelshamy - https://repl.it/ExG4/4

LinkedList.js

function LinkedList(){
  this.head = null;
  this.tail = null;
}

function Node(value, next, prev){
  this.value = value;
  this.next = next;
  this.prev = prev;
}


LinkedList.prototype.addToHead = function(value){
  var newNode = new Node(value, this.head, null);
  //list is not empty;
  if(this.head) this.head.prev = newNode;
  //list is empty so make the head and tail is the new node;
  else this.tail = newNode;
  this.head = newNode;
}

LinkedList.prototype.addToTail = function(value){
  var newNode = new Node(value, null, this.tail);
  if(this.tail) this.tail.next = newNode;
  else this.head = newNode;
  this.tail = newNode;
}

LinkedList.prototype.removeHead = function(){
  //list is empty
  if(!this.head) return null;
  var val  = this.head.value;
  //move current head to the next;
  this.head = this.head.next;
  //list has more than one item ?
  if(this.head) this.head.prev = null;
  else this.tail = null;
  return val;
}

LinkedList.prototype.removeTail = function(){
  if(!this.tail) return null;
  var val  = this.tail.value;
  this.tail = this.tail.prev;
  if(this.tail) this.tail.next = null;
  else this.head = null;
  return val;
}

LinkedList.prototype.search = function(searchValue){
  var currentNode = this.head;
  while(currentNode){
    if (currentNode.value == searchValue) return currentNode.value;
    currentNode = currentNode.next;
  }
  return null;  
}

LinkedList.prototype.indexOf = function(value){
  var currentNode = this.head;
  var indexes = [];
  var currentIndex = 0;
  while(currentNode){
    if (currentNode.value == value) indexes.push(currentIndex) ;
    currentNode = currentNode.next;
    currentIndex++;
  }
  return indexes;  
}


var ll = new LinkedList();

ll.addToHead(123);
ll.addToHead(70);
ll.addToTail('Hello');
ll.addToTail(19);
ll.addToTail('world');
ll.addToTail(20);
ll.addToTail(3000);

console.log(ll.indexOf(20));