From 7c88b2034e47e676c79be6090cb0217d1c3ed8ef Mon Sep 17 00:00:00 2001
From: Yurii Zusik <yurii.zusik@bigcommerce.com>
Date: Mon, 22 Mar 2021 09:41:31 +0200
Subject: [PATCH] feat(storefront): BCTHEME-446 Improve performance of
 analyzing homepage carousel image

---
 .../carousel/utils/getActiveSlideInfo.js      | 10 ++----
 .../carousel/utils/handleImageAspectRatio.js  | 28 +++++++++-------
 .../common/carousel/utils/handleImageLoad.js  | 33 ++++++++++++++++---
 .../stencil/heroCarousel/_heroCarousel.scss   |  9 +++++
 4 files changed, 57 insertions(+), 23 deletions(-)

diff --git a/assets/js/theme/common/carousel/utils/getActiveSlideInfo.js b/assets/js/theme/common/carousel/utils/getActiveSlideInfo.js
index c5b67c770e..3cdf46b7df 100644
--- a/assets/js/theme/common/carousel/utils/getActiveSlideInfo.js
+++ b/assets/js/theme/common/carousel/utils/getActiveSlideInfo.js
@@ -5,16 +5,12 @@ export default ({ $slider }, isAnalyzedDataAttr) => {
     if (isAnalyzedSlide) return { isAnalyzedSlide };
 
     const $activeSlideImg = $activeSlide.find('.heroCarousel-image');
-
-    const attrsObj = {
-        src: $activeSlideImg.attr('src'),
-        srcset: $activeSlideImg.attr('srcset'),
-        sizes: $activeSlideImg.attr('sizes'),
-    };
+    const activeSlideImgNode = $activeSlideImg[0];
 
     return {
-        attrsObj,
         $slider,
         $activeSlide,
+        $activeSlideImg,
+        activeSlideImgNode,
     };
 };
diff --git a/assets/js/theme/common/carousel/utils/handleImageAspectRatio.js b/assets/js/theme/common/carousel/utils/handleImageAspectRatio.js
index ef163e433e..daa28603e4 100644
--- a/assets/js/theme/common/carousel/utils/handleImageAspectRatio.js
+++ b/assets/js/theme/common/carousel/utils/handleImageAspectRatio.js
@@ -17,12 +17,20 @@ const defineClass = (imageAspectRatio) => {
     }
 };
 
+const installClass = (imageNode, $slides) => {
+    if (imageNode.naturalHeight <= 1) return;
+
+    const imageAspectRatio = imageNode.naturalHeight / imageNode.naturalWidth;
+    $slides.each((idx, slide) => $(slide).addClass(defineClass(imageAspectRatio)));
+};
+
 export default ({ delegateTarget }, carousel) => {
     const {
         isAnalyzedSlide,
-        attrsObj,
         $slider,
         $activeSlide,
+        $activeSlideImg,
+        activeSlideImgNode,
     } = getActiveSlideInfo(carousel || delegateTarget.slick, IS_ANALYZED_DATA_ATTR);
 
     if (isAnalyzedSlide) return;
@@ -32,15 +40,11 @@ export default ({ delegateTarget }, carousel) => {
 
     if ($activeSlide.find('.heroCarousel-content').length) return;
 
-    $('<img />')
-        .on('load', function getImageSizes() {
-            const imageHeight = this.height;
-            const imageWidth = this.width;
-
-            if (imageHeight < 2 || imageWidth < 2) return;
-
-            const imageAspectRatio = imageHeight / imageWidth;
-            $activeSlideAndClones.each((idx, slide) => $(slide).addClass(defineClass(imageAspectRatio)));
-        })
-        .attr(attrsObj);
+    if (activeSlideImgNode.complete) {
+        if (activeSlideImgNode.naturalHeight === 1) {
+            $activeSlideAndClones.each((idx, slide) => $(slide).data(IS_ANALYZED_DATA_ATTR, false));
+        } else if (activeSlideImgNode.naturalHeight > 1) {
+            installClass(activeSlideImgNode, $activeSlideAndClones);
+        }
+    } else $activeSlideImg.on('load', () => installClass(activeSlideImgNode, $activeSlideAndClones));
 };
diff --git a/assets/js/theme/common/carousel/utils/handleImageLoad.js b/assets/js/theme/common/carousel/utils/handleImageLoad.js
index 66572db108..9c6f6b0b3c 100644
--- a/assets/js/theme/common/carousel/utils/handleImageLoad.js
+++ b/assets/js/theme/common/carousel/utils/handleImageLoad.js
@@ -3,18 +3,43 @@ import getActiveSlideInfo from './getActiveSlideInfo';
 const IMAGE_ERROR_CLASS = 'is-image-error';
 const IS_ANALYZED_DATA_ATTR = 'image-load-analyzed';
 
+const generateImage = ($slide, $image) => {
+    $('<img />')
+        .on('error', () => $slide.addClass(IMAGE_ERROR_CLASS))
+        .attr({
+            src: $image.attr('src'),
+            srcset: $image.attr('srcset'),
+            sizes: $image.attr('sizes'),
+        });
+};
+
 export default (e, carousel) => {
     const {
         isAnalyzedSlide,
-        attrsObj,
         $activeSlide,
+        $activeSlideImg,
+        activeSlideImgNode,
     } = getActiveSlideInfo(carousel, IS_ANALYZED_DATA_ATTR);
 
     if (isAnalyzedSlide) return;
 
     $activeSlide.data(IS_ANALYZED_DATA_ATTR, true);
 
-    $('<img />')
-        .on('error', () => $activeSlide.addClass(IMAGE_ERROR_CLASS))
-        .attr(attrsObj);
+    if (activeSlideImgNode.complete) {
+        if (activeSlideImgNode.naturalHeight === 0) {
+            $activeSlide.addClass(IMAGE_ERROR_CLASS);
+        } else if (activeSlideImgNode.naturalHeight === 1) {
+            generateImage($activeSlide, $activeSlideImg);
+        }
+
+        return;
+    }
+
+    // if IE
+    if (document.documentMode) {
+        generateImage($activeSlide, $activeSlideImg);
+        return;
+    }
+
+    $activeSlideImg.on('error', () => $activeSlide.addClass(IMAGE_ERROR_CLASS));
 };
diff --git a/assets/scss/components/stencil/heroCarousel/_heroCarousel.scss b/assets/scss/components/stencil/heroCarousel/_heroCarousel.scss
index c109d870eb..10cff12547 100644
--- a/assets/scss/components/stencil/heroCarousel/_heroCarousel.scss
+++ b/assets/scss/components/stencil/heroCarousel/_heroCarousel.scss
@@ -33,6 +33,15 @@
         }
     }
 
+    // for IE
+    @media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {
+        opacity: 0;
+
+        &.slick-initialized {
+            opacity: 1;
+        }
+    }
+
     &:not(.slick-initialized) :not(.heroCarousel-slide--first).heroCarousel-slide {
         display: none;
     }