<label>
  Do heavy work
  <input type="checkbox" id="check" />
</label>

<script>
  // Checbox selection will NOT be responsive
  check.addEventListener("change", (e) => {
    block(5000);
  });
  // This will block the main thread for ~5 seconds
  function block(milliseconds) {
    const start = performance.now();
    while (performance.now() - start < milliseconds) {}
  }
</script>