LayoutShiftAttribution

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

Experimental:This is anexperimental technology
Check theBrowser compatibility table carefully before using this in production.

TheLayoutShiftAttribution interface provides debugging information about elements which have shifted.

Instances ofLayoutShiftAttribution are returned in an array by callingLayoutShift.sources.

Instance properties

LayoutShiftAttribution.nodeRead onlyExperimental: Returns the element that has shifted (null if it has been removed).
LayoutShiftAttribution.previousRectRead onlyExperimental: Returns a DOMRectReadOnly object representing the position of the element before the shift.
LayoutShiftAttribution.currentRectRead onlyExperimental: Returns a DOMRectReadOnly object representing the position of the element after the shift.

Instance methods

LayoutShiftAttribution.toJSON()Experimental: Returns a JSON representation of theLayoutShiftAttribution object.

The following example finds the element with the highest layout shift score, and returns the element in that entry with the largest size prior to the shift (previousRect). For more detail on this seeDebug Web Vitals in the field.

function getCLSDebugTarget(entries) {  const largestEntry = entries.reduce((a, b) =>    a && a.value > b.value ? a : b,  );  if (largestEntry?.sources?.length) {    const largestSource = largestEntry.sources.reduce((a, b) => {      const area = (el) => el.previousRect.width * el.previousRect.height;      return a.node && area(a) > area(b) ? a : b;    });    if (largestSource) {      return largestSource.node;    }  }}