Jquery disable a droppable after it has reached a limit of 3 elements

Question

I have two list boxes that drag and drop I want my second list box to only allow 3 list items from the first list box. My problem is that when I reach the limit it does the counter works but I get this error:

Uncaught Error: cannot call methods on draggable prior to initialization; attempted to call method 'disable'

and it allows it to drag more than 3 elements. I would like it to stop at 3 elements and when I drag out from the second list box it minus the counter.

var counter = 0;

$("#listbox2").droppable({
    drop: function(event, ui) {
        if (counter <= 3) {
            counter++;
            $('#counter_text').text(counter);
        }
        if (counter === 3) {
            $('#listbox2').droppable("disable");
            $('#listbox1 li').draggable("disable");
        }
    }
})

$("#listbox1").droppable({
    drop: function(event, ui) {
        counter--;
        $('#counter_text').text(counter);

    }
})

Answer 1

Yu simply have to initialize the draggable elements. This is a working sample (with an awful styling, BTW)

var counter = 0;
$('#counter_text').text(counter);    

$('#listbox1 li').draggable({
  stop: function(event, ui) {
    $(this).css('left',0);
    $(this).css('top',0);
  }
});

$("#listbox2").droppable({
  drop: function(event, ui) {
    $(this).append(ui.draggable);
    if (counter <= 3) {
      counter++;
      $('#counter_text').text(counter);
    }
    if (counter === 3) {
      $('#listbox2').droppable("disable");
      $('#listbox1 li').draggable("disable");
    }
  },
  hoverClass: 'hover'
});

$("#listbox1").droppable({
  drop: function(event, ui) {
    counter--;
    if (counter<3) {
      $("li").draggable("enable");  
      $('#listbox2').droppable("enable");
    }
    $('#counter_text').text(counter);    
    $(this).append(ui.draggable);
    $(ui.draggable).draggable('enable');
  },
  hoverClass: 'hover'
});

ul {
  border: solid 1px green;
  padding: 5px;
  height: 120px;
}

.hover {
  background-color: #CFC;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.11.4/jquery-ui.js"></script>

<div id="counter_text"></div>

<ul id="listbox1">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li>Item 4</li>
  <li>Item 5</li>
</ul>

<ul id="listbox2">
</ul>