function LinkedList() {
  this.head = null;
  this.tail = null;
  this.length = 0;
}

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

// adds a node to the specified index
// if index is specified, accepts parameter (value, index)
// if no index is specified then add element to the end of list
LinkedList.prototype.add = function(...value) {

  if (!this.head) {
    this.head = this.tail = new Node(...value);
    this.length++;
    return;
  }

  while (value.length) {
    let curr = value.pop();
    this.tail.next = new Node(curr);
    this.tail = this.tail.next;
    this.length++;
  }
}

// retrieves the node at the specified index
LinkedList.prototype.get = function(index) {

  if (index >= this.length) {
    return -1;
  }

  if (index === 0) {
    return this.head;
  }

  let previousNode = null;
  let currentNode = this.head;

  for (let i = 0; i < index; i++) {
    if (!currentNode.next) {
      break;
    }
    previousNode = currentNode;
    currentNode = currentNode.next;
  }

  previousNode.next = currentNode.next;
  this.length--;
  return currentNode;
}

// retrieves and removes the node at the specified index
// if no index is specified, removes the last node (tail)
LinkedList.prototype.remove = function(index) {
  if (this.length === 0) {
    return undefined;
  }

  if (this.head.value === index) {
    this.removeFromHead();
    return this;
  }

  let previousNode = this.head;
  let thisNode = previousNode.next;

  while (thisNode) {
    if (thisNode.value === index) {
      break;
    }

    previousNode = thisNode;
    thisNode = thisNode.next;
  }

  if (thisNode === null) {
    return undefined;
  }

  previousNode.next = thisNode.next;
  this.length--;
  return this;
}

LinkedList.prototype.removeFromHead = function() {
  if (this.length === 0) {
    return undefined;
  }

  const value = this.head.value;
  this.head = this.head.next;
  this.length--;

  return value;
}

let linkedList = new LinkedList()
linkedList.add(0);
linkedList.add(1, 0);
linkedList
console.log(linkedList.remove().value) //should return 1
console.log(linkedList.remove().value) //should return 2