guard against NPEs for IntersectionObserver

routes/_utils/AsyncLayout.js

@@ -14,25 +14,31 @@ class AsyncLayout {
   }
 
   observe(key, node, callback) {
+    if (this._intersectionObserver) {
       this._onIntersectionCallbacks[key] = (entry) => {
         callback(getRectFromEntry(entry))
         this.unobserve(key, node)
       }
       this._intersectionObserver.observe(node)
     }
+  }
 
   unobserve(key, node) {
     if (key in this._onIntersectionCallbacks) {
       return
     }
+    if (this._intersectionObserver) {
       this._intersectionObserver.unobserve(node)
+    }
     delete this._onIntersectionCallbacks[key]
   }
 
   disconnect() {
+    if (this._intersectionObserver) {
       this._intersectionObserver.disconnect()
       this._intersectionObserver = null
     }
   }
+}
 
 export { AsyncLayout }