Fix lazy loading of images in CmsSlot. (#93)

Author: markbrocato

src/CmsSlot.js

@@ -24,7 +24,7 @@ export const styles = theme => ({
         left: 0,
       },
     },
-    '& img[data-rsf-lazy]': {
+    '& img[data-src]': {
       visibility: 'hidden',
     },
   },

src/utils/lazyLoadImages.js

@@ -4,16 +4,25 @@
  * attribute is copied to `src`.
  *
  * See https://developers.google.com/web/fundamentals/performance/lazy-loading-guidance/images-and-video/
+ * @param {DOMElement} element The img element to lazy load
+ * @param {Object} options
+ * @param {Object} options.lazySrcAttribute The attribute containing the image URL. Defaults to `data-src`.
  */
-export default function lazyLoadImages(element, { selector = 'img[data-rsf-lazy]' } = {}) {
+export default function lazyLoadImages(element, { lazySrcAttribute = 'data-src' } = {}) {
   if (!element) return
-  const lazyImages = [...element.querySelectorAll(selector)]
+  const lazyImages = [...element.querySelectorAll(`img[${lazySrcAttribute}]`)]
   if (!lazyImages.length) return
 
   let lazyImageObserver
 
   const load = img => {
-    img.src = img.dataset.src
+    const src = img.getAttribute(lazySrcAttribute)
+    const onload = () => {
+      img.removeAttribute(lazySrcAttribute)
+      img.removeEventListener('load', onload)
+    }
+    img.addEventListener('load', onload)
+    img.setAttribute('src', src)
 
     if (lazyImageObserver) {
       lazyImageObserver.disconnect(img)

test/utils/lazyLoadImages.test.js

@@ -12,7 +12,7 @@ describe('lazyLoadImages', () => {
 
     return (
       <div ref={ref}>
-        <img ref={imageRef} data-src="https://via.placeholder.com/600x600" data-rsf-lazy="1" />
+        <img ref={imageRef} data-src="https://via.placeholder.com/600x600" />
       </div>
     )
   }
@@ -38,7 +38,7 @@ describe('lazyLoadImages', () => {
   })
 
   it('should do nothing if selector can not find anything', () => {
-    selector = { selector: 'test' }
+    selector = { lazySrcAttribute: 'data-lazy-src' }
 
     wrapper = mount(<Test />)
 
@@ -53,10 +53,10 @@ describe('lazyLoadImages', () => {
     // Not intersected
     observer.simulateChange(0, imageRef.current)
     expect(ref.current.src).toBeUndefined()
-
     observer.simulateChange(1, imageRef.current)
-
-    expect(imageRef.current.src).toBe('https://via.placeholder.com/600x600')
+    expect(imageRef.current.getAttribute('src')).toBe('https://via.placeholder.com/600x600')
+    imageRef.current.dispatchEvent(new Event('load'))
+    expect(imageRef.current.getAttribute('data-src')).toBe(null)
   })
 
   describe('if intersection observer is not available', () => {