LinkedListUsage.js

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

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

LinkedList.prototype.addToHead = function ( value ) {
  var newNode = new Node( null, null, value );

  if ( this.head ) {
    newNode.next = this.head
    this.head.prev = newNode;
    this.head = newNode;
  } else {
    this.head = newNode;
    this.tail = newNode;
  }
}

LinkedList.prototype.addToTail = function ( value ) {
  var newNode = new Node( null, null, value );

  if ( this.tail ) {
    newNode.prev = this.tail
    this.tail.next = newNode;
    this.tail = newNode;
  } else {
    this.head = newNode;
    this.tail = newNode;
  }
}

LinkedList.prototype.printAllNodes = function() {
  currentNode = this.head;
  while ( currentNode ) {
    console.log( currentNode.value );
    currentNode = currentNode.next;
  }
}

var arr = [1, 2, 2, 3, 1, 4, 5, 5, 5, 5, 7, 2, 2];

function getResult( arr ) {
  var ll = new LinkedList();

  arr.forEach( function(el){
    ll.addToTail( el );
  });

  var result = [];
  var currentNode = ll.head;
  var currentTotalValue = 1;
  
  while( currentNode ) {
    if ( currentNode.prev && currentNode.value === currentNode.prev.value ) {
      currentTotalValue ++;
    } else {
      var item = currentNode.prev ? currentNode.prev.value : currentNode.value;
      result.push( currentTotalValue > 1 ? item + ':' + currentTotalValue : item );
      currentTotalValue = 1;
    }

    currentNode = currentNode.next;
  }

  return result;
}

getResult(arr);