The previousRect read-only property of the LayoutShiftAttribution interface returns a DOMRectReadOnly object representing the position of the element before the shift.

A DOMRectReadOnly object.

The following example prints the previousRect of the first item in LayoutShift.sources to the console.

new PerformanceObserver((list) => {
  for (const { sources } of list.getEntries()) {
    if (sources) {
      console.log(sources[0].previousRect);
    }
  }
}).observe({ type: "layout-shift", buffered: true });