PerformanceElementTiming.naturalWidth

The naturalWidth read-only property of the PerformanceElementTiming interface returns the intrinsic width of the image element.

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.

In this example the image file has a width of 1000px and a height of 750px. Calling entry.naturalWidth returns 1000, that being the intrinsic width in pixels.

<img src="image.jpg" alt="a nice image" elementtiming="big-image" id="myImage">

const observer = new PerformanceObserver((list) => {
  let entries = list.getEntries().forEach(function (entry) {
    if (entry.identifier === "big-image") {
      console.log(entry.naturalWidth);
    }
  });
});
observer.observe({ entryTypes: ["element"] });