fix: audit incorrectly flagging images as above the fold (#10891) (#1…

…1617)

* fix: audit incorrectly flagging images as above the fold (#10891)

Previously used �lement.offsetTop to find the y position of the image, which does not work when the element parent has a position: relative property.
Instead, this uses �lement.getBoundingClientRect().y top get real y position of the image.
There's one issue though, which is that getBoundingClientRect returns the position relative to the user's viewport, not the absolute position.
So, add window.scrollY to the value to cancel that effect out, and you have the element's absolute position.

https://developer.mozilla.org/en-US/docs/Web/API/Element/getBoundingClientRect
https://developer.mozilla.org/en-US/docs/Web/API/Window/scrollY

* chore: add changeset

.changeset/shy-bees-look.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix toolbar audit incorrectly flagging images as above the fold.

packages/astro/src/runtime/client/dev-toolbar/apps/audit/rules/perf.ts

@@ -36,7 +36,8 @@ export const perf: AuditRuleWithSelector[] = [
 		match(element) {
 			const htmlElement = element as HTMLImageElement | HTMLIFrameElement;
 			// Ignore elements that are above the fold, they should be loaded eagerly
-			if (htmlElement.offsetTop < window.innerHeight) return false;
+			const elementYPosition = htmlElement.getBoundingClientRect().y + window.scrollY 
+			if (elementYPosition < window.innerHeight) return false;
 
 			// Ignore elements using `data:` URI, the `loading` attribute doesn't do anything for these
 			if (htmlElement.src.startsWith('data:')) return false;
@@ -54,7 +55,8 @@ export const perf: AuditRuleWithSelector[] = [
 			const htmlElement = element as HTMLImageElement | HTMLIFrameElement;
 
 			// Ignore elements that are below the fold, they should be loaded lazily
-			if (htmlElement.offsetTop > window.innerHeight) return false;
+			const elementYPosition = htmlElement.getBoundingClientRect().y + window.scrollY 
+			if (elementYPosition > window.innerHeight) return false;
 
 			// Ignore elements using `data:` URI, the `loading` attribute doesn't do anything for these
 			if (htmlElement.src.startsWith('data:')) return false;