The PerformanceObserverEntryList interface is a list of performance events that were explicitly observed via the observe() method.

PerformanceObserverEntryList.getEntries()

Returns a list of all explicitly observed PerformanceEntry objects.

PerformanceObserverEntryList.getEntriesByType()

Returns a list of all explicitly observed PerformanceEntry objects of the given entry type.

PerformanceObserverEntryList.getEntriesByName()

Returns a list of all explicitly observed PerformanceEntry objects based on the given name and entry type.

In the following example, list is the PerformanceObserverEntryList object. The getEntries() method is called to get all explicitly observed PerformanceEntry objects which are "measure" and "mark" in this case.

function perfObserver(list, observer) {
  list.getEntries().forEach((entry) => {
    if (entry.entryType === "mark") {
      console.log(`${entry.name}'s startTime: ${entry.startTime}`);
    }
    if (entry.entryType === "measure") {
      console.log(`${entry.name}'s duration: ${entry.duration}`);
    }
  });
}
const observer = new PerformanceObserver(perfObserver);
observer.observe({ entryTypes: ["measure", "mark"] });