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HTML

              
                <h2>MutationObserver Example - attributeFilter with subtree</h2>

<p>This page uses the MutationObserver API to watch for changes to the DOM tree. In this case, the MutationObserver is looking for specific HTML attributes to be changed on the targeted element, and the same attributes on the target's child elements.</p>

<p>A "Start..." and a "Stop..." button are used to start and stop the MutationObserver. Console messages are displayed specifying which change took place and whether the MutationObserver is started or stopped.</p>

<p id="myParagraph" class="paragraph">This paragraph element will be observed for <strong class="child">changes to its attributes</strong>.</p>

<p><button class="btnStart">Start Observing for Mutations</button>
  <button class="btnStop" disabled>Stop Observing for Mutations</button></p>

<p><select>
  <option>hidden</option>
  <option>data-par</option>
  <option>draggable</option>
</select>

  <button class="btnAttr">Toggle Selected Attribute on Parent</button></p>

<p><select>
  <option>hidden</option>
  <option>data-par</option>
  <option>draggable</option>
</select>

  <button class="btnAttr2">Toggle Selected Attribute on Child</button></p>


              
            
!

CSS

              
                body {
  padding: 0 20px;
  font-size: 1.2em;
}

.paragraph {
  border: dashed 3px #aaa;
  padding: 7px;
}

button {
  margin: 3px;
}
              
            
!

JS

              
                let mPar = document.getElementById('myParagraph'),
    mStrong = document.querySelector('.child'),
    btnAttr = document.querySelector('.btnAttr'),
    btnAttr2 = document.querySelector('.btnAttr2'),
    btnStart = document.querySelector('.btnStart'),
    btnStop = document.querySelector('.btnStop'),
    options = {
      attributes: true,
      attributeFilter: ['hidden', 'contenteditable', 'data-par'],
      subtree: true
    },
    observer = new MutationObserver(mCallback);

function mCallback (mutations) {
  for (let mutation of mutations) {
    if (mutation.type === 'attributes') {
      console.log(`Mutation Detected: Valid attribute has been toggled. Attribute name is: ${mutation.attributeName}.`);
    }
  }
}

function doLogAndBtn(msg) {
  console.log(msg);
  btnStart.disabled = !btnStart.disabled;
  btnStop.disabled = !btnStop.disabled;
}

btnStart.addEventListener('click', function () {
  observer.observe(mPar, options);
  doLogAndBtn('Observing for mutations: STARTED');
}, false);

btnStop.addEventListener('click', function () {
  observer.disconnect();
  doLogAndBtn('Observing for mutations: STOPPED');
}, false);

btnAttr.addEventListener('click', function () {
  mPar.toggleAttribute(document.querySelector('select').value.toString());
}, false);

btnAttr2.addEventListener('click', function () {
  mStrong.toggleAttribute(document.querySelectorAll('select')[0].value.toString());
}, false);
              
            
!
999px

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