App.js

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * @format
 * @flow
 */

import React, {Component} from 'react';
import {Platform, StyleSheet, Text, View, Alert } from 'react-native';
import { WebView } from 'react-native-webview';

type Props = {};
export default class App extends Component<Props> {
  onMessage = (event) => {
    const {title, message} = JSON.parse(event.nativeEvent.data)
    Alert.alert(
      title,
      message,
      [],
      { cancelable: true }
    );
  }

  render() {
    const params = 'platform='+Platform.OS;
    const sourceUri = (Platform.OS === 'android' ? 'file:///android_asset/' : '') + 'Web.bundle/loader.html';
    const injectedJS = `if (!window.location.search) {
      var link = document.getElementById('progress-bar');
      link.href = './site/index.html?${params}';
      link.click();
    }`;


    return (
      <View style={styles.container}>
        <WebView          
          injectedJavaScript={injectedJS}
          source={{ uri: sourceUri }}
          javaScriptEnabled={true}
          originWhitelist={['*']}
          allowFileAccess={true}
          onMessage={this.onMessage}
        />
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1
  }
});