Please report: excessive number of pending callbacks: 501. some pending callbacks that might have leaked by never being called from native code

Query: please report – excessive number of pending callbacks: 501. Some pending callbacks might have leaked by never being called from native code.

When you receive the error message about an excessive number of pending callbacks, it means that there have been a large number of asynchronous operations or callbacks that were not handled properly. This can lead to memory leaks and impact the performance of your application.

To better explain this issue, let’s consider an example:

<script>
  function fetchData(url) {
    return new Promise((resolve, reject) => {
      const xhr = new XMLHttpRequest();
      xhr.open('GET', url, true);
      xhr.onload = function() {
        if (xhr.status === 200) {
          resolve(xhr.responseText);
        } else {
          reject(new Error(xhr.statusText));
        }
      };
      xhr.onerror = function() {
        reject(new Error('Network Error'));
      };
      xhr.send();
    });
  }
  
  function handleData(data) {
    // Do something with the data
  }
  
  fetchData('https://api.example.com/data')
    .then(handleData)
    .catch(error => console.error(error));
</script>

In the above example, we have a function fetchData that makes an asynchronous request to retrieve data from a URL. The retrieved data is then passed to the handleData function for further processing.

If multiple requests are made without properly handling the callbacks, it can lead to an excessive number of pending callbacks.

To fix this issue and prevent memory leaks, you should ensure that all callbacks are called or handled appropriately:

<script>
  // ...
  
  let requestCounter = 0;
  
  function fetchData(url) {
    const requestId = ++requestCounter;
    return new Promise((resolve, reject) => {
      const xhr = new XMLHttpRequest();
      xhr.open('GET', url, true);
      xhr.onload = function() {
        if (xhr.status === 200) {
          resolve(xhr.responseText);
        } else {
          reject(new Error(xhr.statusText));
        }
        handleCallback(requestId); // Call the callback handler after resolving or rejecting
      };
      xhr.onerror = function() {
        reject(new Error('Network Error'));
        handleCallback(requestId); // Call the callback handler after rejecting
      };
      xhr.send();
    });
  }
  
  function handleData(data) {
    // Do something with the data
  }
  
  function handleCallback(requestId) {
    // Handle the callback, e.g.: logging, cleaning up, etc.
    console.log('Callback handled for request ID:', requestId);
  }
  
  fetchData('https://api.example.com/data')
    .then(handleData)
    .catch(error => console.error(error));
</script>

In the improved example, we introduced a handleCallback function which is called after resolving or rejecting the XHR request. This ensures that the callbacks are properly handled regardless of the outcome. Additionally, we added a request ID to track each request and handle the corresponding callback.

Remember to adapt this solution to your specific use case and the environment you are working with. A similar approach can be applied for other asynchronous operations to handle the callbacks properly and avoid the error message about an excessive number of pending callbacks.