Interactive elements in popup respond to input within 100ms

Interactive elements that freeze for more than 100ms after a click break the user's perception of control. Per ISO 25010:2011 performance-efficiency.time-behaviour, 100ms is the threshold beyond which lag becomes noticeable. In practice, synchronous XHR or large inline loops in click handlers block the UI thread entirely — buttons appear stuck, users double-click, and duplicate actions trigger. Extensions with this pattern see disproportionate negative reviews relative to their functional quality.

Move expensive work out of the click handler's synchronous path: disable the button immediately, show a loading state, then offload computation to the background service worker via chrome.runtime.sendMessage.

button.addEventListener('click', async () => {
  button.disabled = true;
  button.textContent = 'Processing...';

  const result = await chrome.runtime.sendMessage({ type: 'PROCESS_DATA' });

  button.disabled = false;
  button.textContent = 'Done';
  displayResult(result);
});

For CPU-intensive work that must stay in the popup context, consider a Web Worker. Synchronous XMLHttpRequest must be eliminated unconditionally — it blocks the entire browser UI thread.