Double Linked List

linkedList.md

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

function ListNode(val, next=null, previous=null) {
  this.val = val;
  this.next = next;
  this.previous = previous;
}


LinkedList.prototype.unshift = function(node) {
  node.next = this.head;
  node.previous = null;
  if(this.head){this.head.previous = node;}
    else {this.tail = node;}
  this.head = node;
  
};

LinkedList.prototype.pop = function() {
  let node = this.tail;
  if(node.previous)
  { 
    node.previous.next = null;
    this.tail = node.previous;
    
  } else {
    this.tail = null;
    this.head = null;
    
  }
  node.previous = null;
  return node;
  
};

LinkedList.prototype.push = function(node) {
  node.previous = this.tail || null;
  node.next = null;
  (this.tail) ? this.tail.next = node : this.head = node;
  this.tail = node;
  
};

LinkedList.prototype.shift = function() {
  let node = this.head;
  if (this.head.next) {node.next.previous = null;}
    else{ this.tail = null; }  
  this.head = this.head.next;
  node.next = null;
  return node;
  
};

LinkedList.prototype.search = function(query) {
  let current = this.head;
  while(current){
    if (current.val === query){
      return current;
    }
    current = current.next;
  }
  return null;
}

LinkedList.prototype.indexOf = function(val){
  const ans = [];
  let indx = 0;
  let current = this.head;
  
  while(current){
    if(current.val === val){
      ans.push(indx);
    }
    current = current.next;
    indx++;
  }
  return ans;
};

const ll = new LinkedList();
const firstNode = new ListNode(1);
const secondNode = new ListNode(5);
const thirdNode = new ListNode(3);

ll.push(firstNode);
ll.push(secondNode);
ll.push(thirdNode);
ll.push(new ListNode(5));
ll.push(new ListNode(8));
ll.push(new ListNode(7));
ll.push(new ListNode(5));



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