Open met de inspector tools van je browser de console tab en plak de onderstaande code.

try {
  // Create the performance observer.
  const po = new PerformanceObserver((list) => {
    for (const entry of list.getEntries()) {
      // Log the entry and all associated details.
  // Start listening for `longtask` entries to be dispatched.
  po.observe({type: 'longtask', buffered: true});
} catch (e) {
  console.log(`The browser doesn't support this API`)