🐛 [amp-carousel 0.1] Fix snapping and closing race (#32695)

* Init * init * Fix race
ampproject · Feb 23, 2021 · 8fa011f · 8fa011f
1 parent 5cb3446
commit 8fa011f
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diff --git a/extensions/amp-carousel/0.1/slidescroll.js b/extensions/amp-carousel/0.1/slidescroll.js
@@ -521,6 +521,11 @@ export class AmpSlideScroll extends BaseSlides {
    * @return {number} a number representing the next slide index.
    */
   getNextSlideIndex_(currentScrollLeft) {
+    // Addresses race where slideWidth is 0, due to being hidden
+    // while snapping is occuring.
+    if (!currentScrollLeft && !this.slideWidth_) {
+      return 0;
+    }
     // This can be only 0, 1 or 2, since only a max of 3 slides are shown at
     // a time.
     const scrolledSlideIndex = Math.round(currentScrollLeft / this.slideWidth_);

diff --git a/extensions/amp-carousel/0.1/test/test-slidescroll.js b/extensions/amp-carousel/0.1/test/test-slidescroll.js
@@ -1271,6 +1271,17 @@ describes.realWin(
         expect(showSlideSpy).to.have.been.calledWith(4);
       });
 
+      it('should handle carousel snapping & hiding race', async () => {
+        const ampSlideScroll = await getAmpSlideScroll(true);
+        const impl = await ampSlideScroll.getImpl();
+
+        // simluate carousel hidding
+        impl.slideWidth_ = 0;
+
+        // simulate snapping
+        expect(impl.getNextSlideIndex_(0)).to.equal(0);
+      });
+
       it('should NOT call showSlide_ before layout', async () => {
         const ampSlideScroll = await getAmpSlideScroll(
           true,