Create your first app

Initialize a new Expo app

We'll use create-expo-app to initialize a new Expo app. It is a command line tool to create a new React Native project. Run the following command in your terminal:

This command will create a new project directory named StickerSmash, using the default template. This template has essential boilerplate code and libraries needed to build our app, including Expo Router. We'll continue to add more libraries throughout this tutorial as needed.

Download assets

After downloading the archive:

1. Unzip the archive and replace the default assets in the your-project-name/assets/images directory.
2. Open the project directory in a code editor or IDE.

Run reset-project script

In this tutorial, we'll build our app from scratch and understand the fundamentals of adding a file-based navigation. Let's run the reset-project script to remove the boilerplate code:

After running the above command, there are two files (index.tsx and _layout.tsx) left inside the app directory. The other directories (components, constants, and hooks) also contain boilerplate code. We can delete all files inside these directories because we'll create our own components.

Run the app on mobile and web

In the project directory, run the following command to start the development server from the terminal:

After running the above command:

1. The development server will start, and you'll see a QR code inside the terminal window.
2. Scan that QR code to open the app on the device. On Android, use the Expo Go > Scan QR code option. On iOS, use the default camera app.
3. To run the web app, press w in the terminal. It will open the web app in the default web browser.

Once it is running on all platforms, the app should look like this:

Edit the index screen

The app/index.tsx file defines the text displayed on the app's screen. It is the entry point of our app and executes when the development server starts. It uses core React Native components such as <View> and <Text> to display background and text.

Styles applied to these components use JavaScript objects rather than CSS, which is used on web. However, a lot of the properties will look familiar if you've previously used CSS on web. Most React Native components accept a style prop that accepts a JavaScript object as its value. For more details, see Styling in React Native.

Let's modify app/index.tsx screen:

1. Import StyleSheet from react-native and create a styles object to define our custom styles.
2. Add a styles.container.backgroundColor property to <View> with the value of #25292e. This changes the background color.
3. Replace the default value of <Text> with "Home screen".
4. Add a styles.text.color property to <Text> with the value of #fff (white) to change the text color.

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

export default function Index() {
  return (
    <View style={styles.container}>
      <Text style={styles.text}>Home screen</Text>
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#25292e',
    alignItems: 'center',
    justifyContent: 'center',
  },
  text: {
    color: '#fff',
  },
});

React Native uses the same color format as the web. It supports hex triplets (this is what #fff is), rgba, hsl, and named colors, such as red, green, blue, peru, and papayawhip. For more information, see Colors in React Native.

This change will reflect on all platforms automatically: