React Native the polyglot platform 2

alter-app.js

// @flow
import React, { Component } from "react";
import { NativeModules, StyleSheet, Text, View } from "react-native";
type Props = {};
type State = { message: string };
const { HelloWorld } = NativeModules;
export default class App extends Component<Props, State> {
  state = {
    message: "loading..."
  };
  async componentDidMount() {
    try {
      const message = await HelloWorld.sayHello();
      this.setState({
        message
      });
    } catch(e) {
      alert(e);
    }
  }
  render() {
    const { message } = this.state;
    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>Message from Native:</Text>
        <Text style={styles.welcome}>"{message}"</Text>
      </View>
    );
  }
}
const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: "center",
    alignItems: "center",
    backgroundColor: "#F5FCFF"
  },
  welcome: {
    fontSize: 20,
    textAlign: "center",
    margin: 10
  }
});