App.js

import React from 'react';
import { StyleSheet, Text, View } from 'react-native';

class SplashScreen extends React.Component {
  render() {
    const viewStyles = [styles.container, { backgroundColor: 'orange' }];
    const textStyles = {
      color: 'white',
      fontSize: 40,
      fontWeight: 'bold'
    };

    return (
      <View style={viewStyles}>
        <Text style={textStyles}>
          Splash Screen
        </Text>
      </View>
    );
  }
}

export default class App extends React.Component {
  constructor(props) {
    super(props);

    this.state = { isLoading: true }
  }

  performTimeConsumingTask = async() => {
    return new Promise((resolve) =>
      setTimeout(
        () => { resolve('result') },
        2000
      )
    );
  }

  async componentDidMount() {
    // Preload data from an external API
    // Preload data using AsyncStorage
    const data = await this.performTimeConsumingTask();

    if (data !== null) {
      this.setState({ isLoading: false });
    }
  }

  render() {
    if (this.state.isLoading) {
      return <SplashScreen />;
    }

    return (
      <View style={styles.container}>
        <Text style={styles.welcome}>
          Welcome to React Native!
        </Text>
        <Text style={styles.instructions}>
          Reload the App to see a splash screen
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
  instructions: {
    textAlign: 'center',
    color: '#333333',
    marginBottom: 5,
  },
});