MutationObserver 没有在子节点上拾取

Question

小提琴：https://jsfiddle.net/7gj26hqu/

我希望有一个MutationObserver 可以检测其自身内的所有新节点。在示例中，我设置了{childList: true, subtree: true}，但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任何深度？

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

看起来当被观察的容器设置了innerHTML 时，容器的子级被清空，然后完整地添加新的子级。使用同步观察者（以便您可以看到正在发生的事情），查看添加元素时子节点是如何存在的：

// 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>

正在观察的容器的孙子对象在子对象被附加到容器之前被附加到子对象，因此subtree: true 看不到附加操作。

要检测以这种方式插入的所有子节点，您必须手动递归遍历 MutationRecord 中的所有元素，尽管subtree: true。

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：

如果您想改用 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>