Improve ui & performance

app/src/components/helper/isElementInViewport.ts

@@ -0,0 +1,12 @@
+declare const window: any
+declare const document: any
+
+export function isElementInViewport(el: any) {
+  const rect = el.getBoundingClientRect()
+  return (
+        rect.top >= 0 &&
+        rect.left >= 0 &&
+        rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
+        rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
+  )
+}