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) {
  let newNode = new Node(value, this.head, null);
  if (this.head) this.head.prev = newNode;
  else this.tail = newNode;
  this.head = newNode;
};

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

LinkedList.prototype.removeTail = function() {
if(!this.tail) return null;
let 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) {
let currentNode = this.head;
while (currentNode) {
  if(currentNode.value === searchValue) return currentNode.value;
  currentNode = currentNode.next;
}
return null;
}

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


let myLL = new LinkedList();

myLL.addToTail(1);
myLL.addToTail(5);
myLL.addToTail(3);
myLL.addToTail(5);
myLL.addToTail(8);
myLL.addToTail(7);
myLL.addToTail(5);

console.log(myLL.indexOf(5));