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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
interface has two methods. The Performance
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
interface has two properties. The Performance
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
property returns a navigation
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.
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.