Add Long Task script

Author: nucliweb

README.md

@@ -355,3 +355,24 @@ timingOptions.forEach((timing) => {
 
 console.table(calculateTimings("first", "REQ_START_UNTIL_RES_END"));
 ```
+## Interaction
+
+### Long Task
+
+To determine when long tasks happen, you can use [PerformanceObserver](https://developer.mozilla.org/docs/Web/API/PerformanceObserver) and register to observe entries of type `longtask`:
+
+```js
+try {
+ // Create the performance observer.
+ const po = new PerformanceObserver((list) => {
+ for (const entry of list.getEntries()) {
+ // Log the entry and all associated details.
+ console.table(entry.toJSON());
+ }
+ });
+ // 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`)
+}
+```