PerformanceElementTiming

The aim of the Element Timing API is to give web developers or analytics tools the ability to measure rendering timestamps of critical elements on a page.

The API supports timing information on the following elements:

• <img> elements,
• <image> elements inside an <svg>,
• poster images of <video> elements,
• elements which have a contentful background-image property with a URL value for a resource that is actually available, and
• groups of text nodes, such as a <p>.

The author flags an element for observation by adding the elementtiming attribute on the element.

PerformanceElementTiming inherits from PerformanceEntry.

This interface extends the following PerformanceEntry properties for event timing performance entry types by qualifying them as follows:

PerformanceEntry.durationRead onlyExperimental

Always returns 0 as duration does not apply to this interface.

PerformanceEntry.entryTypeRead onlyExperimental

Always returns "element".

PerformanceEntry.nameRead onlyExperimental

Returns "image-paint" for images and "text-paint" for text.

PerformanceEntry.startTimeRead onlyExperimental

Returns the value of this entry's renderTime if it is not 0, otherwise the value of this entry's loadTime.

This interface also supports the following properties:

PerformanceElementTiming.elementRead onlyExperimental

An Element representing the element we are returning information about.

PerformanceElementTiming.idRead onlyExperimental

A string which is the id of the element.

PerformanceElementTiming.identifierRead onlyExperimental

A string which is the value of the elementtiming attribute on the element.

PerformanceElementTiming.intersectionRectRead onlyExperimental

A DOMRectReadOnly which is the rectangle of the element within the viewport.

PerformanceElementTiming.loadTimeRead onlyExperimental

A DOMHighResTimeStamp with the loadTime of the element.

PerformanceElementTiming.naturalHeightRead onlyExperimental

An unsigned 32-bit integer (unsigned long) which is the intrinsic height of the image if this is applied to an image, 0 for text.

PerformanceElementTiming.naturalWidthRead onlyExperimental

An unsigned 32-bit integer (unsigned long) which is the intrinsic width of the image if this is applied to an image, 0 for text.

PerformanceElementTiming.renderTimeRead onlyExperimental

A DOMHighResTimeStamp with the renderTime of the element.

PerformanceElementTiming.urlRead onlyExperimental

A string which is the initial URL of the resources request for images, 0 for text.

PerformanceElementTiming.toJSON()Experimental

Returns a JSON representation of the PerformanceElementTiming object.

In this example two elements are being observed by adding the elementtiming attribute. A PerformanceObserver is registered to get all performance entries of type "element" and the buffered flag is used to access data from before observer creation.

<img src="image.jpg" elementtiming="big-image" /> <p elementtiming="text" id="text-id">text here</p> 

const observer = new PerformanceObserver((list) => { list.getEntries().forEach((entry) => { console.log(entry); }); }); observer.observe({ type: "element", buffered: true }); 

Two entries will be output to the console. The first containing details of the image, the second with details of the text node.

• elementtiming HTML attribute