fix: scroll back to position 0 after an element screenshot

.changeset/element-scroll-back-to-top.md

@@ -0,0 +1,7 @@
+---
+"@wdio/image-comparison-core": patch
+---
+
+fix: scroll back to position 0 after an element screenshot
+
+With `autoElementScroll` enabled, `checkElement`, `saveElement` and `toMatchElementSnapshot` scroll the element into view and then scroll back to the old position. When the old position was 0 (the top of the page), the page was not scrolled back, because 0 was treated as "no position". A later `checkScreen` then captured a scrolled page. The position is now restored whenever it was read, also when it is 0.

packages/image-comparison-core/src/methods/takeElementScreenshots.test.ts

@@ -121,6 +121,16 @@ describe('takeElementScreenshot', () => {
             expect(waitForSpy).toHaveBeenCalledWith(100)
         })
 
+        it('should restore scroll to position 0 when the page was at the top', async () => {
+            const optionsWithScroll = { ...baseOptions, autoElementScroll: true }
+            executeMock.mockResolvedValueOnce(0) // previous scroll position at the top
+
+            await takeElementScreenshot(browserInstance, optionsWithScroll, true)
+
+            expect(executeMock).toHaveBeenCalledTimes(2)
+            expect(executeMock.mock.calls[1][1]).toBe(0)
+        })
+
         it('should not restore scroll when autoElementScroll is enabled but no previous position', async () => {
             const optionsWithScroll = { ...baseOptions, autoElementScroll: true }
             executeMock.mockResolvedValueOnce(undefined) // no previous position
@@ -224,6 +234,16 @@ describe('takeElementScreenshot', () => {
             )
         })
 
+        it('should restore scroll to position 0 in viewport mode when the page was at the top', async () => {
+            const vpScrollOptions: ElementScreenshotDataOptions = { ...vpOptions, autoElementScroll: true }
+            executeMock.mockResolvedValueOnce(0) // previous scroll position at the top
+
+            await takeElementScreenshot(browserInstance, vpScrollOptions, true)
+
+            expect(executeMock).toHaveBeenCalledTimes(2)
+            expect(executeMock.mock.calls[1][1]).toBe(0)
+        })
+
         it('should use origin: document for the default (no biDiOrigin set)', async () => {
             const defaultOptions = { ...vpOptions, biDiOrigin: undefined }
 
@@ -304,6 +324,16 @@ describe('takeElementScreenshot', () => {
             expect(waitForSpy).toHaveBeenCalledWith(100)
         })
 
+        it('should scroll back to position 0 when the page was at the top', async () => {
+            const optionsWithScroll = { ...baseOptions, autoElementScroll: true }
+            executeMock.mockResolvedValueOnce(0) // previous scroll position at the top
+
+            await takeElementScreenshot(browserInstance, optionsWithScroll, false)
+
+            expect(executeMock).toHaveBeenCalledTimes(2)
+            expect(executeMock.mock.calls[1][1]).toBe(0)
+        })
+
         it('should not scroll back when autoElementScroll is enabled but no current position', async () => {
             const optionsWithScroll = { ...baseOptions, autoElementScroll: true }
             executeMock.mockResolvedValueOnce(undefined) // no scroll position returned

packages/image-comparison-core/src/methods/takeElementScreenshots.ts

@@ -51,7 +51,7 @@ async function takeBiDiElementScreenshot(
         clip,
     })
 
-    if (options.autoElementScroll && currentPosition) {
+    if (options.autoElementScroll && typeof currentPosition === 'number') {
         await browserInstance.execute(scrollToPosition, currentPosition)
     }
 
@@ -120,7 +120,7 @@ async function takeBiDiElementScreenshotFromViewport(
         clip,
     })
 
-    if (options.autoElementScroll && currentPosition) {
+    if (options.autoElementScroll && typeof currentPosition === 'number') {
         await browserInstance.execute(scrollToPosition, currentPosition)
     }
 
@@ -179,7 +179,7 @@ async function takeWebDriverElementScreenshot(
     // When the screenshot has been taken and the element position has been determined,
     // we can scroll back to the original position
     // We don't need to wait for the scroll here because we don't take a screenshot after this
-    if (options.autoElementScroll && currentPosition) {
+    if (options.autoElementScroll && typeof currentPosition === 'number') {
         await browserInstance.execute(scrollToPosition, currentPosition)
     }