fix(useVisibilityChange): useEffect return null & destroy is not a fu…

…nction form UT with jest (#730)

packages/react-vant/src/components/hooks/use-visibility-change.ts

@@ -9,34 +9,33 @@ export default function useVisibilityChange(
   const [state, setState] = useState<boolean>()
   useEffect(() => {
     // compatibility: https://caniuse.com/#feat=intersectionobserver
-    if (!inBrowser || !window.IntersectionObserver) {
-      return null
-    }
-    const observer = new IntersectionObserver(
-      entries => {
-        // visibility changed
-        onChange?.(entries[0].intersectionRatio > 0)
-        for (const entry of entries) {
-          setState(entry.isIntersecting)
-        }
-      },
-      { root: document.body }
-    )
+    if (!(!inBrowser || !window.IntersectionObserver)) {
+      const observer = new IntersectionObserver(
+        entries => {
+          // visibility changed
+          onChange?.(entries[0].intersectionRatio > 0)
+          for (const entry of entries) {
+            setState(entry.isIntersecting)
+          }
+        },
+        { root: document.body }
+      )
 
-    const observe = () => {
-      if (target.current) {
-        observer.observe(target.current)
+      const observe = () => {
+        if (target.current) {
+          observer.observe(target.current)
+        }
       }
-    }
 
-    const unobserve = () => {
-      if (target.current) {
-        observer.unobserve(target.current)
+      const unobserve = () => {
+        if (target.current) {
+          observer.unobserve(target.current)
+        }
       }
-    }
 
-    observe()
-    return unobserve
+      observe()
+      return unobserve
+    }
   }, [target.current])
 
   return [state] as const