What is the best approach for monitoring read-only attributes of an HTMLElement using JavaScript?

Question

What is the best approach for monitoring read-only attributes of an HTMLElement using JavaScript?

When attempting to observe the "isConnected" property of an HTMLElement, I found that it is a read-only property and there is no propertyDescriptor for it. This means that the traditional method of overriding getters and setters or creating a proxy object is not applicable.

I have learned about mutationObserver, but it seems they can only observe attributes. Additionally, they are resource-intensive for our application since we need to observe the "isConnected" property on every dynamically created element (80% of our application consists of dynamic elements).

Are there any alternative methods for observing changes to read-only properties?

javascript dom observers mutation-observers dom-node

Answer 1

Answer №1

If the original poster wants to monitor DOM changes dynamically, they may want to consider using the MutationObserver API. While the OP may not be able to directly observe a node's isConnected attribute, they can still obtain similar information about whether a node is part of the rendered DOM by listening for a 'childList' mutation type.

function handleDomChanges(mutationsList, observer) {
  for (const mutation of mutationsList) {
  debugger;
    const {
      type, attributeName,
      addedNodes, removedNodes
    } = mutation;
    if (type === 'childList') {
      if (addedNodes.length >= 1) {

        console.log(`${ addedNodes.length } child node(s) has/have been added`);
      }
      if (removedNodes.length >= 1) {

        console.log(`${ removedNodes.length } child node(s) has/have been removed`);
      }
    } else if (type === 'attributes') {
      console.log(`The ${ attributeName } attribute has been mutated.`);
    }
  }
};

const config = {
  attributes: true,
  childList: true,
  subtree: true
};
const targetNode = document.querySelector('#app');

const observer = new MutationObserver(handleDomChanges);

observer.observe(targetNode, config);
// observer.disconnect();


const listNode = document.querySelector('#navList');

const itemNode = document.createElement('li');
const testNode = document.createElement('a');
testNode.href = '\/';
testNode.textContent = 'test 4';

itemNode.appendChild(testNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});
listNode.appendChild(itemNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});
testNode.remove(); 

console.log({
  testNodeIsConnected: testNode.isConnected
});
itemNode.appendChild(testNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});

.as-console-wrapper {
  bottom: 0;
  left: auto!important;
  min-height: 100%;
  width: 50%;
}

<div id='app'>
  <nav>
    <ul id="navList">
      <li><a href="/">test 1</a></li>
      <li><a href="/">test 2</a></li>
      <li><a href="/">test 3</a></li>
    </ul>
  </nav>
</div>

Answer 2

If the original poster wants to monitor DOM changes dynamically, they may want to consider using the MutationObserver API. While the OP may not be able to directly observe a node's isConnected attribute, they can still obtain similar information about whether a node is part of the rendered DOM by listening for a 'childList' mutation type.

function handleDomChanges(mutationsList, observer) {
  for (const mutation of mutationsList) {
  debugger;
    const {
      type, attributeName,
      addedNodes, removedNodes
    } = mutation;
    if (type === 'childList') {
      if (addedNodes.length >= 1) {

        console.log(`${ addedNodes.length } child node(s) has/have been added`);
      }
      if (removedNodes.length >= 1) {

        console.log(`${ removedNodes.length } child node(s) has/have been removed`);
      }
    } else if (type === 'attributes') {
      console.log(`The ${ attributeName } attribute has been mutated.`);
    }
  }
};

const config = {
  attributes: true,
  childList: true,
  subtree: true
};
const targetNode = document.querySelector('#app');

const observer = new MutationObserver(handleDomChanges);

observer.observe(targetNode, config);
// observer.disconnect();


const listNode = document.querySelector('#navList');

const itemNode = document.createElement('li');
const testNode = document.createElement('a');
testNode.href = '\/';
testNode.textContent = 'test 4';

itemNode.appendChild(testNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});
listNode.appendChild(itemNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});
testNode.remove(); 

console.log({
  testNodeIsConnected: testNode.isConnected
});
itemNode.appendChild(testNode);

console.log({
  testNodeIsConnected: testNode.isConnected
});

.as-console-wrapper {
  bottom: 0;
  left: auto!important;
  min-height: 100%;
  width: 50%;
}

<div id='app'>
  <nav>
    <ul id="navList">
      <li><a href="/">test 1</a></li>
      <li><a href="/">test 2</a></li>
      <li><a href="/">test 3</a></li>
    </ul>
  </nav>
</div>

What is the best approach for monitoring read-only attributes of an HTMLElement using JavaScript?

Answer №1

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