Document: drag イベント

<div class="dropzone">
  <div id="draggable" draggable="true">
    This div is draggable
  </div>
</div>
<div class="dropzone"></div>

body {
  /* Prevent the user selecting text in the example */
  user-select: none;
}

#draggable {
  text-align: center;
  background: white;
}

.dropzone {
  width: 200px;
  height: 20px;
  background: blueviolet;
  margin: 10px;
  padding: 10px;
}

.dropzone.dragover {
  background-color: purple;
}

.dragging {
  opacity: .5;
}

let dragged;

/* events fired on the draggable target */
document.addEventListener("drag", event => {
  console.log("dragging");
});

document.addEventListener("dragstart", event => {
  // store a ref. on the dragged elem
  dragged = event.target;
  // make it half transparent
  event.target.classList.add("dragging");
});

document.addEventListener("dragend", event => {
  // reset the transparency
  event.target.classList.remove("dragging");
});

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

document.addEventListener("dragenter", event => {
  // highlight potential drop target when the draggable element enters it
  if (event.target.classList.contains("dropzone")) {
    event.target.classList.add("dragover");
  }
});

document.addEventListener("dragleave", event => {
  // reset background of potential drop target when the draggable element leaves it
  if (event.target.classList.contains("dropzone")) {
    event.target.classList.remove("dragover");
  }
});

document.addEventListener("drop", event => {
  // prevent default action (open as link for some elements)
  event.preventDefault();
  // move dragged element to the selected drop target
  if (event.target.classList.contains("dropzone")) {
    event.target.classList.remove("dragover");
    dragged.parentNode.removeChild(dragged);
    event.target.appendChild(dragged);
  }
});