As u can see, images swap positions correctly but when i want to drag the image in the blank space (i want to make this image the latest in the row) it crashes.

 function allowDrop(ev) {
   ev.preventDefault();
}

function drag(ev) {
   ev.dataTransfer.setData("text", ev.target.id);
}

function drop(ev) {
   ev.preventDefault();

   var id = ev.dataTransfer.getData("text");
   var element = document.getElementById(id)
   var div = document.getElementById(id).parentNode;
   var clonedHeart = document.getElementById(ev.target.id).cloneNode(true);

   ev.target.parentNode.insertBefore(element, ev.target.id.nextSibling)
   document.getElementById(ev.target.id).remove();
   div.appendChild(clonedHeart);

   ev.dataTransfer.clearData();
}

Any help? Ty in advance. Here u got the JSFiddle