how to make an element draggable javascript code example

Example: js draggable

<script>
  var dragged;

  /* events fired on the draggable target */
  document.addEventListener("drag", function(event) {

  }, false);

  document.addEventListener("dragstart", function(event) {
    // store a ref. on the dragged elem
    dragged = event.target;
    // make it half transparent
    event.target.style.opacity = .5;
  }, false);

  document.addEventListener("dragend", function(event) {
    // reset the transparency
    event.target.style.opacity = "";
  }, false);

  /* events fired on the drop targets */
  document.addEventListener("dragover", function(event) {
    // prevent default to allow drop
    event.preventDefault();
  }, false);

  document.addEventListener("dragenter", function(event) {
    // highlight potential drop target when the draggable element enters it
    if (event.target.className == "dropzone") {
      event.target.style.background = "purple";
    }

  }, false);

  document.addEventListener("dragleave", function(event) {
    // reset background of potential drop target when the draggable element leaves it
    if (event.target.className == "dropzone") {
      event.target.style.background = "";
    }

  }, false);

  document.addEventListener("drop", function(event) {
    // prevent default action (open as link for some elements)
    event.preventDefault();
    // move dragged elem to the selected drop target
    if (event.target.className == "dropzone") {
      event.target.style.background = "";
      dragged.parentNode.removeChild( dragged );
      event.target.appendChild( dragged );
    }
  }, false);

</script>