The PerformanceElementTiming
interface contains render timing information for image and text node elements the developer annotated with an elementtiming
attribute for observation.
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:
The author flags an element for observation by adding the elementtiming
attribute on the element.
PerformanceElementTiming
inherits from PerformanceEntry
.
PerformanceEntry PerformanceElementTiming
This interface extends the following PerformanceEntry
properties for event timing performance entry types by qualifying them as follows:
PerformanceEntry.duration
Read only Experimental
Always returns 0
as duration
does not apply to this interface.
PerformanceEntry.entryType
Read only Experimental
Always returns "element"
.
PerformanceEntry.name
Read only Experimental
Returns "image-paint"
for images and "text-paint"
for text.
PerformanceEntry.startTime
Read only Experimental
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.element
Read only Experimental
An Element
representing the element we are returning information about.
PerformanceElementTiming.id
Read only Experimental
A string which is the id
of the element.
PerformanceElementTiming.identifier
Read only Experimental
A string which is the value of the elementtiming
attribute on the element.
PerformanceElementTiming.intersectionRect
Read only Experimental
A DOMRectReadOnly
which is the rectangle of the element within the viewport.
PerformanceElementTiming.loadTime
Read only Experimental
A DOMHighResTimeStamp
with the loadTime of the element.
PerformanceElementTiming.naturalHeight
Read only Experimental
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.naturalWidth
Read only Experimental
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.renderTime
Read only Experimental
A DOMHighResTimeStamp
with the renderTime of the element.
PerformanceElementTiming.url
Read only Experimental
A string which is the initial URL of the resources request for images, 0 for text.
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.