PerformanceObserver() constructor creates a new PerformanceObserver object with the given observer callback. The observer callback is invoked when performance entry events are recorded for the entry types that have been registered, via the observe() method.getEntries() method of the PerformanceObserverEntryList interface returns a list of explicitly observed performance entry objects for a given filter. The list's members are determined by the set of entry types specified in the call to the observe() method. The list is available in the observer's callback function (as the first parameter in the callback).getEntriesByName() method of the PerformanceObserverEntryList interface returns a list of explicitly observed performance entry objects for a given name and entry type. The list's members are determined by the set of entry types specified in the call to the observe() method. The list is available in the observer's callback function (as the first parameter in the callback).getEntriesByType() method of the PerformanceObserverEntryList returns a list of explicitly observed performance entry objects for a given performance entry type. The list's members are determined by the set of entry types specified in the call to the observe() method. The list is available in the observer's callback function (as the first parameter in the callback).Navigator interface represents the state and the identity of the user agent. It allows scripts to query it and to register themselves to carry on some activities.navigator.sendBeacon() method can be used to asynchronously transfer a small amount of data over HTTP to a web server.Performance interface represents timing-related performance information for the given page.Performance.now() method returns a DOMHighResTimeStamp, measured in milliseconds, accurate to one thousandth of a millisecond.