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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

            
              <h2>MutationObserver Example - Recording an Old Attribute Value</h2>

<p>This page uses the MutationObserver API to watch for changes to the <code>data-name</code> attribute on the specified paragraph element. When the <code>data-name</code> attribute is changed by the user, the <code>mutation.oldValue</code> property is used to record the previous value of the attribute each time it's changed.</p>

<p id="myParagraph" data-name="Example" class="paragraph">This paragraph element will be observed for changes to a <code>data-*</code> attribute.</p>

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

<p><input type="text" placeholder="Enter some text">
  <button class="btnAttr">Change the Data Attribute Value</button></p>


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

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

button {
  margin: 3px;
}
            
          
!
            
              let mPar = document.getElementById('myParagraph'),
    btnAttr = document.querySelector('.btnAttr'),
    btnStart = document.querySelector('.btnStart'),
    btnStop = document.querySelector('.btnStop'),
    input = document.querySelector('input'),
    options = {
      attributes: true,
      attributeOldValue: true
    },
    observer = new MutationObserver(mCallback);

function mCallback (mutations) {
  for (let mutation of mutations) {
    if (mutation.type === 'attributes') {
      console.log(`Mutation Detected: An attribute has been added or removed. The attribute name is: ${mutation.attributeName}, old value is ${mutation.oldValue}.`);
    }
  }
}

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);

btnAttr.addEventListener('click', function () {
  mPar.dataset.name = input.value;
}, false);

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