Metro bundler not starting when running run-android / run-ios command on linux in Facebook React Native

Explanation of the problem

Problem Statement: When executing the react-native run-android command, the message displayed is that the Metro Bundler (JS server) is starting, but it does not actually start, resulting in the failure to launch the application in the emulator. However, running the command react-native start separately resolves the issue. It is assumed that this issue might apply to react-native run-ios as well, but this needs to be confirmed.

Environment Information:

• React Native version: 0.62.2
• @react-native-community/cli: 4.8.0
• node: 12
• System: Ubuntu 18.04

Steps to Reproduce:

• Create a React Native project with the mentioned environment information on a Linux machine
• Execute the command react-native run-android

Expected Results:

• The Metro Bundler should start when executing react-native run-android if it’s not already started in a separate terminal window.
• If there is an issue with the Metro Bundler, the primary process should display errors indicating why the bundler failed to start.

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Problem solution for Metro bundler not starting when running run-android / run-ios command on linux in Facebook React Native

If you’re having trouble running the run-android or run-ios command and Metro bundler is not starting in Facebook React Native, here are a few steps you can try to resolve the issue:

1. Check if your environment variables are set up correctly: Make sure that you have set up all required environment variables for React Native, including ANDROID_HOME and JAVA_HOME on Linux.
2. Check if you have the latest version of React Native: Make sure that you have the latest version of React Native installed on your system.
3. Restart the Metro bundler: Sometimes, restarting the Metro bundler can resolve issues. You can do this by running the react-native start command in the terminal.
4. Delete the node_modules directory: Deleting the node_modules directory and reinstalling the dependencies can resolve issues with the Metro bundler.
5. Clear the cache: Clearing the cache can resolve issues with the Metro bundler. You can do this by running the react-native start --reset-cache command in the terminal.
6. Check for compatibility issues: Make sure that you are using a version of React Native that is compatible with your operating system and the version of Java and Android Studio that you have installed.

Other popular problems with Facebook React Native

To resolve this issue, developers can follow the following steps:

• Ensure that the development server is running on the same network as the device or emulator
• Check for the correct IP address and port configuration in the Metro Bundler
• Disable any firewall restrictions on the network
• If the issue still persists, try connecting the device or emulator to a different network.

A brief introduction to Facebook React Native

Facebook React Native is an open-source framework for building mobile applications using JavaScript and React. It allows developers to create native mobile apps for iOS and Android platforms using a single codebase, improving efficiency and reducing the development time. React Native uses native components, which are equivalent to the native UI elements of the underlying platform, ensuring a smooth and efficient user experience.

React Native operates on a JavaScript runtime environment, providing developers with the ability to leverage existing web development skills and tools to create native mobile apps. The framework also utilizes a virtual DOM, similar to the one used in web development, which provides optimized updates and rendering of components. This allows developers to easily create dynamic and responsive user interfaces with a high degree of performance and fluidity. Additionally, React Native includes a rich set of built-in components, APIs, and tools that streamline the development process and make it easier to build high-quality apps.

Most popular use cases for Facebook React Native

1. Building Cross-Platform Mobile Applications: React Native is a popular choice for developers who want to build mobile applications that can run on multiple platforms, such as Android and iOS, with a single codebase. This allows developers to use a single set of components, libraries, and tools to create a seamless user experience across multiple devices, without having to write separate code for each platform.

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

class App extends Component {
  render() {
    return (
      <View style={styles.container}>
        <Text style={styles.text}>
          Hello, React Native!
        </Text>
      </View>
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center'
  },
  text: {
    fontSize: 20,
    fontWeight: 'bold'
  }
});

export default App;