W3Schools Tryit Editor

<!DOCTYPE HTML>
<html>
<style>
.droptarget {
  width: 100px; 
  height: 30px;
  padding: 5px;
  border: 1px solid black;
}
</style>

<body>
<h1>HTML DOM Events</h1>
<h2>The dragstart, dragover, and drop Events</h2>

<p>This example uses the addEventListener() method to attach "dragstart", "dragover" and "drop" events to the document object.</p>

<p>Drag the text back and forth between the two rectangles:</p>

/* Events fired on the drop target */
document.addEventListener("dragover", function(event) {
  event.preventDefault();
});

document.addEventListener("drop", function(event) {
  event.preventDefault();
  var data = event.dataTransfer.getData("Text");
  event.target.appendChild(document.getElementById(data));
  document.getElementById("demo").innerHTML = "The p element was dropped";
});
</script>

</body>

</html>