MutationObserver无法在子节点上启动

Question

小提琴：https://jsfiddle.net/7gj26hqu/

我希望有一个MutationObserver可以检测其内部的所有新节点。在示例中，我设置了{childList: true, subtree: true}，但是div#nested没有出现在MutationObserver中（显示在控制台中）。

如何让观察者检测子节点的深度？

const domObserver = new MutationObserver((records) => {
  records.forEach((record) => {
    console.log(record)
  })
})

domObserver.observe(document.querySelector('#frame'), {childList: true, subtree: true})

// copy child nodes out of #template (as a string) and inject them into #frame for the observer to detect
document.querySelector('#frame').innerHTML = document.querySelector('#template').innerHTML

<div id="frame"></div>

<div id="template" style="display: none;">
   <div class="level-1">
    <div class="level-2">

      <div id="nested">
        I exist in the DOM but am not being seen by the MutationObserver
      </div>

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>
</div>

Answer 1

[似乎正在观察的容器设置为innerHTML，该容器的子容器将被清空，然后添加新的子容器完全完好。使用同步观察器（以便您可以看到正在发生的事情），了解在添加元素时子节点如何存在：

// Look at results in browser console:

window.addEventListener('DOMNodeInserted', (e) => {
  console.log(e.path[0].childNodes.length);
});

document.querySelector('#frame').innerHTML = document.querySelector('#template').innerHTML

<div id="frame"></div>

<div id="template" style="display: none;">
   <div class="level-1">
    <div class="level-2">
    
      <div id="nested">
        I exist in the DOM but am not being seen by the MutationObserver
      </div>
      
    </div>
  </div>
  
  <div class="level-1">
    <div class="level-2">
    
    </div>
  </div>
  
  <div class="level-1">
    <div class="level-2">
    
    </div>
  </div>
</div>

被观察到的容器的孙代已附加到子代之前子代已附加到容器，因此subtree: true看不到附加动作。

要检测以此方式插入的所有子节点，尽管subtree: true，您仍必须手动递归地迭代MutationRecord中的所有元素。

const recurse = (parent) => {
  
  console.log(parent);
  if (parent.childNodes) {
    [...parent.childNodes].forEach(recurse);
  }
};
const domObserver = new MutationObserver((records) => {
  for (const record of records) {
    for (const node of record.addedNodes) {
      recurse(node);
    }
  }
})

domObserver.observe(document.querySelector('#frame'), {childList: true, subtree: true})

// copy child nodes out of #template (as a string) and inject them into #frame for the observer to detect
document.querySelector('#frame').innerHTML = document.querySelector('#template').innerHTML

<div id="frame"></div>

<div id="template" style="display: none;">
   <div class="level-1">
    <div class="level-2">

      <div id="nested">
        I exist in the DOM but am not being seen by the MutationObserver
      </div>

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>
</div>

结果：

如果要使用TreeWalker：

const frame = document.querySelector('#frame');
const domObserver = new MutationObserver(() => {
  // If the container's innerHTML was assigned to, iterate over all descendants:
  const treeWalker = document.createTreeWalker(frame);
  const nodes = [];
  let currentNode = treeWalker.currentNode;
  while (currentNode) {
    nodes.push(currentNode);
    currentNode = treeWalker.nextNode();
  }
  console.log(nodes);
});

domObserver.observe(frame, {
  childList: true,
  subtree: true
})

// copy child nodes out of #template (as a string) and inject them into #frame for the observer to detect
document.querySelector('#frame').innerHTML = document.querySelector('#template').innerHTML

<div id="frame"></div>

<div id="template" style="display: none;">
  <div class="level-1">
    <div class="level-2">

      <div id="nested">
        I exist in the DOM but am not being seen by the MutationObserver
      </div>

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>

  <div class="level-1">
    <div class="level-2">

    </div>
  </div>
</div>