Handling no IntersectionObserver

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-storefront",
-  "version": "8.4.0",
+  "version": "8.5.0",
   "description": "Build and deploy e-commerce progressive web apps (PWAs) in record time.",
   "module": "./index.js",
   "license": "Apache-2.0",

src/LazyHydrate.js

@@ -1,5 +1,6 @@
 import React, { useEffect, useState, useRef } from 'react'
 import PropTypes from 'prop-types'
+import useIntersectionObserver from './hooks/useIntersectionObserver'
 
 import { StylesProvider, createGenerateClassName } from '@material-ui/core/styles'
 import { SheetsRegistry } from 'jss'
@@ -52,18 +53,6 @@ const isBrowser = () => {
   )
 }
 
-// Used for detecting when the wrapped component becomes visible
-const io =
-  isBrowser() && IntersectionObserver
-    ? new IntersectionObserver(entries => {
-        entries.forEach(entry => {
-          if (entry.isIntersecting || entry.intersectionRatio > 0) {
-            entry.target.dispatchEvent(new CustomEvent('visible'))
-          }
-        })
-      })
-    : null
-
 function LazyHydrateInstance({ className, ssrOnly, children, on, index, ...props }) {
   function isHydrated() {
     if (isBrowser()) {
@@ -77,40 +66,52 @@ function LazyHydrateInstance({ className, ssrOnly, children, on, index, ...props
   const childRef = useRef(null)
   const [hydrated, setHydrated] = useState(isHydrated())
 
+  function hydrate() {
+    setHydrated(true)
+    // Remove the server side generated stylesheet
+    const stylesheet = window.document.getElementById(`jss-lazy-${index}`)
+    if (stylesheet) {
+      stylesheet.remove()
+    }
+  }
+
   useEffect(() => {
     setHydrated(isHydrated())
   }, [props.hydrated, ssrOnly])
 
+  if (on === 'visible') {
+    useIntersectionObserver(
+      // As root node does not have any box model, it cannot intersect.
+      () => childRef.current.children[0],
+      (visible, disconnect) => {
+        if (visible) {
+          hydrate()
+          disconnect()
+        }
+      },
+      [],
+      // Fallback to eager hydration
+      () => {
+        hydrate()
+      },
+    )
+  }
+
   useEffect(() => {
     if (hydrated) return
 
-    function hydrate() {
-      setHydrated(true)
-      // Remove the server side generated stylesheet
-      const stylesheet = window.document.getElementById(`jss-lazy-${index}`)
-      if (stylesheet) {
-        stylesheet.remove()
-      }
-    }
-
-    let el
-    if (on === 'visible') {
-      if (io && childRef.current.childElementCount) {
-        // As root node does not have any box model, it cannot intersect.
-        el = childRef.current.children[0]
-        io.observe(el)
-      }
+    if (on === 'click') {
+      childRef.current.addEventListener('click', hydrate, {
+        once: true,
+        capture: true,
+        passive: true,
+      })
     }
 
-    childRef.current.addEventListener(on, hydrate, {
-      once: true,
-      capture: true,
-      passive: true,
-    })
-
     return () => {
-      if (el) io.unobserve(el)
-      childRef.current.removeEventListener(on, hydrate)
+      if (on === 'click') {
+        childRef.current.removeEventListener('click', hydrate)
+      }
     }
   }, [hydrated, on])
 

src/hooks/useIntersectionObserver.js

@@ -1,4 +1,11 @@
-import React, { useEffect } from 'react'
+import { useEffect } from 'react'
+
+function getElement(ref) {
+  if (ref && ref.current) {
+    return ref.current
+  }
+  return ref
+}
 
 /**
  * Calls a provided callback when the provided element moves into or out of the viewport.
@@ -25,21 +32,25 @@ import React, { useEffect } from 'react'
  *
  * ```
  *
- * @param {Function} getRef A function that returns a ref pointing to the element to observe
+ * @param {Function} getRef A function that returns a ref pointing to the element to observe OR the element itself
  * @param {Function} cb A callback to call when visibility changes
  * @param {Object[]} deps The IntersectionObserver will be updated to observe a new ref whenever any of these change
+ * @param {Function} notSupportedCallback Callback fired when IntersectionObserver is not supported
  */
-export default function useIntersectionObserver(getRef, cb, deps) {
+export default function useIntersectionObserver(getRef, cb, deps, notSupportedCallback) {
   useEffect(() => {
+    if (!window.IntersectionObserver) {
+      notSupportedCallback &&
+        notSupportedCallback(new Error('IntersectionObserver is not available'))
+      return
+    }
     const observer = new IntersectionObserver(entries => {
       // if intersectionRatio is 0, the element is out of view and we do not need to do anything.
       cb(entries[0].intersectionRatio > 0, () => observer.disconnect())
     })
-
-    const ref = getRef()
-
-    if (ref && ref.current) {
-      observer.observe(ref.current)
+    const el = getElement(getRef())
+    if (el) {
+      observer.observe(el)
       return () => observer.disconnect()
     }
   }, deps)

test/hooks/useIntersectionObserver.test.js

@@ -45,4 +45,32 @@ describe('useIntersectionObserver', () => {
       mount(<Test />)
     }).not.toThrowError()
   })
+
+  describe('when IntersectionObserver is not supported', () => {
+    let IntersectionObserver
+
+    beforeEach(() => {
+      IntersectionObserver = window.IntersectionObserver
+      delete window.IntersectionObserver
+    })
+
+    afterEach(() => {
+      window.IntersectionObserver = IntersectionObserver
+    })
+
+    it('should call the not supported callback', () => {
+      const notSupported = jest.fn()
+
+      const Test = () => {
+        useIntersectionObserver(() => null, jest.fn(), [], notSupported)
+        return <div />
+      }
+
+      expect(() => {
+        mount(<Test />)
+      }).not.toThrowError()
+
+      expect(notSupported).toHaveBeenCalled()
+    })
+  })
 })