The Performance Timeline API defines extensions to the
Performance interface to support client-side latency measurements within applications. The extensions provide interfaces to retrieve performance entry metrics based on specific filter criteria. The standard also includes interfaces that allow an application to define performance observer callbacks that are notified when specific performance events are added to the browser's performance timeline.
This document provides an overview of the standard's interfaces. For more details about the interfaces, see the reference pages and Using Performance Timeline.
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The Performance Timeline API extends the
Performance interface with three methods that provide different mechanisms to get a set of
performance records (metrics), depending on the specified filter criteria. The methods are:
PerformanceEntry interface encapsulates a single performance entry — that is, a single data point or metric in the performance timeline. This interface has the following four properties, and these properties are extended (with additional constraints) by other interfaces (such as
The name of the performance entry when the metric was created.
The type of performance metric (for example, "
high resolution timestamprepresenting the starting time for the performance entry.
A high resolution timestamp representing the time value of the duration of the performance event. (Some performance entry types have no concept of duration and this value is set to
'0'for such types.)
The performance observer interfaces allow an application to register an observer for specific performance event types, and when one of those event types is recorded, the application is notified of the event via the observer's callback function that was specified when the observer was created.
When the observer (callback) is invoked, the callback's parameters include a
performance observer entry list that contains only observed
performance entries. That is, the list contains entries only for the event types that were specified when the observer's
observe() method was invoked. The
performance observer entry list interface has the same three
getEntries*() methods as the
Performance interface. However, note there is one key difference with these methods; the
performance observer entry list versions are used to retrieve observed performance entries within the observer callback.
observe() method (which is used to register the
entry types to observe), the
PerformanceObserver interface also has a
disconnect() method that stops an observer from receiving further events.
Performance observers were added to the
Level 2 version of the standard and were not widely implemented.
|Performance Timeline |
A summary of the interfaces' implementation status is provided below, including a link to more detailed information.
- Performance interface extensions: As shown in the
Performanceinterface's Browser Compatibility table, most of these interfaces are broadly implemented by desktop browsers and have less support on mobile devices.
- PerformanceEntry: As shown in the
PerformanceEntryinterface's Browser Compatibility table, most of these interfaces are broadly implemented by desktop browsers and have less support on mobile devices.
- Performance Observers
: As shown in the
PerformanceObserverinterface's Browser Compatibility table, this interface has no shipping implementations.
To test your browser's support for these interfaces, run the