PerformanceScriptTiming

Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The PerformanceScriptTiming interface is specified in the Long Animation Frames API and provides metrics on individual scripts that contribute to long animation frames (LoAFs).

Description

Long animation frames (LoAFs) are rendering updates that are delayed beyond 50ms. LoAFs can result in slow user interface (UI) updates, making controls appear unresponsive and causing janky (non-smooth) animated effects and scrolling. This often leads to user frustration.

The PerformanceScriptTiming interface (instances of which are accessed via the PerformanceLongAnimationFrameTiming.scripts property) provides the following granular set of information on individual scripts that contribute to LoAFs, allowing developers to narrow down their root causes:

A detailed set of timestamps for each script.
The identity and type of the invoker, i.e., the feature that, when invoked, ran the script.
Detailed information on each script source file, including the URL, and the function name and character position that contributed to the LoAF.

PerformanceScriptTiming inherits from PerformanceEntry.

Instance properties

This interface extends the following PerformanceEntry properties for long animation frame performance entries:

PerformanceEntry.duration Read only: Returns a DOMHighResTimeStamp representing the elapsed time in milliseconds between the start and end of the script's execution.
PerformanceEntry.entryType Read only: Returns the entry type, which is always "script".
PerformanceEntry.name Read only: Returns the entry name, which is always "script".
PerformanceEntry.startTime Read only: Returns a DOMHighResTimeStamp representing the time when the script execution started, in milliseconds.

This interface also supports the following properties:

PerformanceScriptTiming.executionStart Read only: Returns a DOMHighResTimeStamp indicating the time when the script compilation finished and execution started.
PerformanceScriptTiming.forcedStyleAndLayoutDuration Read only: Returns a DOMHighResTimeStamp indicating the total time spent, in milliseconds, by the script processing forced layout/style. See Avoid layout thrashing to understand what causes this.
PerformanceScriptTiming.invoker Read only: Returns a string value indicating the identity of the feature that, when invoked, ran the script.
PerformanceScriptTiming.invokerType Read only: Returns a string value indicating the type of feature that, when invoked, ran the script.
PerformanceScriptTiming.pauseDuration Read only: Returns a DOMHighResTimeStamp indicating the total time, in milliseconds, spent by the script on "pausing" synchronous operations (for example, Window.alert() calls or synchronous XMLHttpRequests).
PerformanceScriptTiming.sourceCharPosition Read only: Returns a number representing the script character position of the script feature that contributed to the LoAF.
PerformanceScriptTiming.sourceFunctionName Read only: Returns a string representing the name of the function that contributed to the LoAF.
PerformanceScriptTiming.sourceURL Read only: Returns a string representing the URL of the script.
PerformanceScriptTiming.window Read only: Returns a reference to a Window object representing the window of the container (i.e., either the top-level document or an <iframe>) in which the LoAF-causing script was executed.
PerformanceScriptTiming.windowAttribution Read only: Returns an enumerated value describing the relationship of the container (i.e., either the top-level document or an <iframe>) in which the LoAF-causing script was executed, relative to the window running the current document.

Instance methods

PerformanceScriptTiming.toJSON(): Returns a JSON representation of the PerformanceScriptTiming object.

Examples

See Long animation frame timing for examples related to the Long Animation Frames API.

Specifications

Long Animation Frames API