Long Task
To determine when long tasks happen, you can use PerformanceObserver (opens in a new tab) and register to observe entries of type longtask:
Snippet
try { const po = new PerformanceObserver((list) => { const numLongTasks = list.getEntries().length; for (const entry of list.getEntries()) { console.table(entry.toJSON()); } console.log( `%cNum. Long Tasks: ${numLongTasks}`, "color: #FF4E42; font-weight: bold", ); }); po.observe({ type: "longtask", buffered: true }); } catch (e) { console.error(`The browser doesn't support this API`); }