DOM event when element is removed

2020-07-18 08:59发布

站内问答 / JavaScript
1325 2 6

Is there any way to get notification when an element is removed from the DOM, either directly or as part of a subtree? It seems like the only methods available are just for directly removed nodes, but I would like to get a notification when a whole subtree that contains my node is removed.

EDIT

Seems the problem wasn't entirely clear, so I have made a challenge: https://jsbin.com/winukaf

The DOM looks like this:

<body>
  <div class="root">
    <div class="great-grand-parent">
      <div class="grand-parent">
        <div class="parent">
          <div class="leaf">
            Am I still here?
          </div>
        </div>
      </div>
    </div>
  </div>
</body>

and the challenge is to notify when any one of the elements here are removed, since that will remove the leaf node from the DOM tree.

2条回答
SAY GOODBYE
2楼-- · 2020-07-18 09:39

You should use the MutationObserver API to accomplish this. Here's MDN's example adapted to a simple scenario:

// Select the node that will be observed for mutations
var targetNode = document.getElementsByClassName('root')[0];

// Options for the observer (which mutations to observe)
var config = {
  childList: true,
  subtree: true
};

// Callback function to execute when mutations are observed
var callback = function(mutationsList, observer) {
  console.log('A child node has been added or removed.');
  console.log(mutationsList[0]);
};

// Create an observer instance linked to the callback function
var observer = new MutationObserver(callback);

// Start observing the target node for configured mutations
observer.observe(targetNode, config);

var subElement = document.getElementsByClassName('parent')[0];
var elementToRemove = document.getElementsByClassName('leaf')[0];
var anotherElement = document.getElementsByClassName('great-grand-parent')[0];
setTimeout(function() {
  subElement.removeChild(elementToRemove);
}, 500);
setTimeout(function() {
  targetNode.removeChild(anotherElement);
}, 500);

// Later, you can stop observing
// observer.disconnect();
<div class="root">
  <div class="great-grand-parent">
    <div class="grand-parent">
      <div class="parent">
        <div class="leaf">
          Am I still here?
        </div>
      </div>
    </div>
  </div>
</div>

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贼婆χ
3楼-- · 2020-07-18 09:57

There's a HTML5 API called MutationObserver and it has pretty good support

Here's an example:

// Element is the whatever subtree/element you need to watch over
var in_dom = document.body.contains(element);
var observer = new MutationObserver(function(mutations) {
    if (document.body.contains(element)) {
        if (!in_dom) {
            console.log("element inserted");
        }
        in_dom = true;
    } else if (in_dom) {
        in_dom = false;
        console.log("element removed");
    }

});
observer.observe(document.body, {childList: true, subtree: true});
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