How to use Javascript's Performance API and measure page performance

The High Resolution Time standard defines a

Performance

interface that supports client-side latency measurements within applications. The

Performance

interfaces are considered high resolution because they are accurate to a thousandth of a millisecond (subject to hardware or software constraints). The interfaces support a number of use cases including calculating frame-rates (potentially important in animations) and benchmarking (such as the time to load a resource).

Since a platform's system clock is subject to various skews (such as NTP adjustments), the interfaces support a monotonic clock i.e. a clock that is always increasing. As such, the

Performance

API defines a

DOMHighResTimeStamp

type rather than using the

Date.now()

interface.

DOMHighResTimeStamp

The

DOMHighResTimeStamp

type, as its name implies, represents a high resolution point in time. This type is a

double

and is used by the performance interfaces. The value could be a discrete point in time or the difference in time between two discrete points in time.

The unit of

DOMHighResTimeStamp

is milliseconds and should be accurate to 5 µs (microseconds). However, If the browser is unable to provide a time value accurate to 5 microseconds (because, for example, due to hardware or software constraints), the browser can represent a the value as a time in milliseconds accurate to a millisecond.

Methods

The

Performance

interface has two methods. The

now()

method returns a

DOMHighResTimeStamp

whose value that depends on the

navigation start

and scope. If the scope is a window, the value is the time the browser context was created and if the scope is a

worker

, the value is the time the worker was created.

The

toJSON()

method returns a serialization of the

Performance

object, for those attributes that can be serialized.

Properties

The

Performance

interface has two properties. The

timing

property returns a

PerformanceTiming

object containing latency-related performance information such as the start of navigation time, start and end times for redirects, start and end times for responses, etc.

The

navigation

property returns a

PerformanceNavigation

object representing the type of navigation that occurs in the given browsing context, such as the page was navigated to from history, the page was navigated to by following a link, etc.

Interfaces

Performance

Provides methods and properties containing timing-related performance information for the given page.

PerformanceEntry

Provides methods and properties the encapsulate a single performance metric that is part of the performance timeline.

PerformanceFrameTiming

Provides methods and properties containing frame timing data about the browser's event loop.

PerformanceMark

An abstract interface for

performance entries

with an

entry type

of "

mark

". Entries of this type are created by calling

performance.mark()

to add a named

DOMHighResTimeStamp

(the mark) to the browser's performance timeline.

PerformanceMeasure

An abstract interface for

performance entries

with an

entry type

of "

measure

". Entries of this type are created by calling

performance.measure()

to add a named

DOMHighResTimeStamp

(the measure) between two marks to the browser's performance timeline.

PerformanceNavigationTiming

Provides methods and properties to store and retrieve

high resolution timestamps

or metrics regarding the browser's document navigation events.

PerformanceObserver

Provides methods and properties used to observe performance measurement events and be notified of new performance entries as they are recorded in the browser's performance timeline.

PerformanceResourceTiming

Provides methods and properties for retrieving and analyzing detailed network timing data regarding the loading of an application's resources.

Specifications

Implementation status

As shown in the

Performance

interface's Browser Compatibility table, most of these interfaces are broadly implemented by desktop browsers.

To test your browser's support for the

Performance

interface, run the

perf-api-support

application.

See also

• A Primer for Web Performance Timing APIs

Credits

• Source: https://developer.mozilla.org/en-US/docs/Web/API/Performance_API
• Published under Open CC Attribution ShareAlike 3.0 licence