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.

Performance extensions


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:
getEntries()
Returns all recorded 
performance entries
 or, optionally, the entries based on the specified 
name
, 
performance type
 and/or the 
initiatorType
 (such as an HTML element).
getEntriesByName()
Returns the recorded 
performance entries
 based on the specified name and optionally the 
performance type
.
getEntriesByType()
Returns the recorded 
performance entries
 based on the specified 
performance type
.

PerformanceEntry interface

The 
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 
PerformanceMark
):
name
The name of the performance entry when the metric was created.
entryType
The type of performance metric (for example, "
mark
").
startTime
A 
high resolution timestamp
 representing the starting time for the performance entry.
duration
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.)

This interface includes a 
toJSON()
 method that returns the serialization of the 
PerformanceEntry
 object. The serialization is specific to the performance entry's 
type
.

Performance observers

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
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.
Besides the 
PerformanceObserver's
 interface's 
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.

Implementation status

A summary of the interfaces' implementation status is provided below, including a link to more detailed information.
To test your browser's support for these interfaces, run the 
perf-api-support
 application.

See Also

Credits