To ensure web applications are fast, it's important to measure and analyze various performance metrics. The Performance API provides important built-in metrics and the ability to add your own measurements to the browser's performance timeline. The performance timeline contains high precision timestamps and can be displayed in developer tools. You can also send its data to analytics end points to record performance metrics over time.
Each performance metric is represented by a single PerformanceEntry
. A performance entry has a name
, a duration
, a startTime
, and a type
. All performance metrics extend the PerformanceEntry
interface and qualify it further.
Most of the performance entries are recorded for you without you having to do anything, and are then accessible either through Performance.getEntries()
or (preferably) through PerformanceObserver
. For example, PerformanceEventTiming
entries are recorded for events that take longer than a set threshold. But the Performance API also enables you to define and record your own custom events, using the PerformanceMark
and PerformanceMeasure
interfaces.
The main Performance
interface is available in both Window
and Worker
global scopes, and enables you to add custom performance entries, to clear performance entries, and to retrieve performance entries.
The PerformanceObserver
interface enables you to listen for various types of performance entry as they are recorded.
For more conceptual information, see the Performance API guides below.