Fixed the Function Component Example (#2019)

* Fixed the Function Component Example

We experienced that the documentation was faulty so after we at @enpit found a fix, we wanted to share it with you. 
The old trigger `appState.current.match(/inactive|background/) && nextAppState === "active"` would never work because the useState hook doesn't update the state fast enough for the function to work. The solution is to use useRef instead and optional (to display the inactive status under iOS) also use a `useState` for cosmetics.

* removed block comment, removed spaces

* rephrase and move new comment, add one more sentence, prettier run

* language lint fix

Co-authored-by: Bartosz Kaszubowski <gosimek@gmail.com>

docs/appstate.md

@@ -36,30 +36,37 @@ To see the current state, you can check `AppState.currentState`, which will be k
 <block class="functional syntax" />
 
 ```SnackPlayer name=AppState%20Function%20Component%20Example
-import React, { useEffect, useRef } from "react";
+import React, { useRef, useState, useEffect } from "react";
 import { AppState, StyleSheet, Text, View } from "react-native";
 
 const AppStateExample = () => {
   const appState = useRef(AppState.currentState);
+  const [appStateVisible, setAppStateVisible] = useState(appState.current);
 
   useEffect(() => {
     AppState.addEventListener("change", _handleAppStateChange);
 
     return () => {
       AppState.removeEventListener("change", _handleAppStateChange);
     };
-  }, [_handleAppStateChange]);
+  }, []);
 
   const _handleAppStateChange = (nextAppState) => {
-    if (appState.current.match(/inactive|background/) && nextAppState === "active") {
+    if (
+      appState.current.match(/inactive|background/) &&
+      nextAppState === "active"
+    ) {
       console.log("App has come to the foreground!");
     }
+
     appState.current = nextAppState;
+    setAppStateVisible(appState.current);
+    console.log("AppState", appState.current);
   };
 
   return (
     <View style={styles.container}>
-      <Text>Current state is: {appState.current}</Text>
+      <Text>Current state is: {appStateVisible}</Text>
     </View>
   );
 };
@@ -68,13 +75,15 @@ const styles = StyleSheet.create({
   container: {
     flex: 1,
     justifyContent: "center",
-    alignItems: "center"
-  }
+    alignItems: "center",
+  },
 });
 
 export default AppStateExample;
 ```
 
+If you don't want to see the AppState update from `active` to `inactive` on iOS you can remove the state variable and use the `appState.current` value.
+
 <block class="classical syntax" />
 
 ```SnackPlayer name=AppState%20Class%20Component%20Example
@@ -126,7 +135,7 @@ export default AppStateExample;
 
 <block class="endBlock syntax" />
 
-This example will only ever appear to say "Current state is: active" because the app is only visible to the user when in the `active` state, and the null state will happen only momentarily.
+This example will only ever appear to say "Current state is: active" because the app is only visible to the user when in the `active` state, and the null state will happen only momentarily. If you want to experiment with the code we recommend to use your own device instead of embedded preview.
 
 ---