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I want to find out when an element is dragged and dropped outside of its parent:

element.addEventListener('dragend', function(event) {
  // check if element is dropped outside its parent
}, false)

I want to find out when an element is dragged and dropped outside of its parent:

element.addEventListener('dragend', function(event) {
  // check if element is dropped outside its parent
}, false)
  • javascript
  • drag-and-drop
Share Improve this question edited Jun 11, 2020 at 17:33 terrymorse 7,1161 gold badge23 silver badges31 bronze badges asked Jun 10, 2020 at 21:25 Bargain23Bargain23 1,9834 gold badges32 silver badges58 bronze badges 0
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This technique identifies whether or not the dragged element was dropped inside its parent by:

  1. storing dragParent element upon 'dragstart'
  2. adding 'drop' event event listener to window
  3. using drop event's event.target to determine drop target
  4. walking up event target's DOM tree to search for dragParent

// the parent of the dragged element
let dragParent = null;

function handleDragstart(ev) {
  // record the dragged element's parent
  dragParent = ev.target.parentElement;

  // set a 'drop' listener to the window
  window.addEventListener('drop', handleDrop);
}

// handle a 'drop' event to the window
function handleDrop(ev) {
  ev.preventDefault();

  // remove the 'drop' listener
  window.removeEventListener('drop', handleDrop);

  // search up target's DOM tree for dragParent
  for (let el = ev.target; el.tagName !== 'HTML'; el = el.parentElement) {
    if (el === dragParent) {
      alert('#p1 was dropped inside dragParent');
      return;
    }
  }
  alert('#p1 was dropped outside dragParent');
}

// these event handers are required to make an element into a drop zone
function handleDragover(ev) {
  ev.preventDefault();
}

function handleDragend(ev) {}

// convert some elements into drop zones
// ref: https://developer.mozilla/en-US/docs/Web/API/HTML_Drag_and_Drop_API#define_a_drop_zone
//
function makeDropZone(el) {
  el.addEventListener('dragover', handleDragover);
  el.addEventListener('drop', handleDragend);
}
for (const elId of ['sibling', 'parent', 'stranger']) {
  const element = document.getElementById(elId);
  makeDropZone(element);
}
makeDropZone(document.body);

// make `#p1` draggable
document.getElementById('p1').addEventListener('dragstart', handleDragstart);
body {
  padding: 0.4rem 0 2rem 0.4rem;
  height: calc(100% - 0.5rem);
  width: calc(100% - 2rem);
  border: 1px solid #888;
  font-family: sans-serif;
}

div {
  padding: 0.6rem;
}

#parent {
  background-color: #ddd;
  width: 90%;
  padding: 0.3rem;
}

#p1 {
  background-color: white;
  padding: 0.1rem;
  width: 30%;
}

#sibling {
  background-color: #bbb;
  width: 50%;
  height: 3rem;
}

#stranger {
  background-color: #ddd;
  margin: 0.5rem 0;
  width: 90%;
  height: 80px;
  padding: 0.3rem;
}
<body>
  body
  <h3>Drag <code>#p1</code> onto <code>#sibling</code>, <code>#parent</code>, or
    <code>body</code></h3>
  <div id="parent">
    #parent
    <p id="p1" draggable="true">
      #p1 (draggable)
    </p>
    <div id="sibling">
      #sibling
    </div>
  </div>
  <div id="stranger">
    #stranger
  </div>
</body>

本文标签： javascriptHow to detect if a dragged element is dropped outside of its parentStack Overflow

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