The LayoutShiftAttribution interface provides debugging information about elements which have shifted.

Instances of LayoutShiftAttribution are returned in an array by calling LayoutShift.sources.

LayoutShiftAttribution.node Read only Experimental

Returns the element that has shifted (null if it has been removed).

LayoutShiftAttribution.previousRect Read only Experimental

Returns a DOMRectReadOnly object representing the position of the element before the shift.

LayoutShiftAttribution.currentRect Read only Experimental

Returns a DOMRectReadOnly object representing the position of the element after the shift.

LayoutShiftAttribution.toJSON() Experimental

Returns a JSON representation of the LayoutShiftAttribution 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 see Debug 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;
    }
  }
}

• Debug layout shifts
• Debug Web Vitals in the field