ReactNative Eject Explained

My understanding is that when you run the "create-react-native-app" (or "expo init" now) you are basically adding the Expo library on top of React Native.

I think the main reason for using Expo is to get your app up and running quickly. I think the main reason to eject is that eventually you might need to do more complicated customization with native code and need more control, etc. Here is a better explanation of Expo vs React Native CLI to bootstrap your app:

https://levelup.gitconnected.com/expo-vs-react-native-cli-a-guide-to-bootstrapping-new-react-native-apps-6f0fcafee58f

When you eject you are returning to the same state as if you did not use Expo to setup your app (native ios/android projects will be generated, etc.)

Here are a few other links that helped me understand: http://www.reactnativeexpress.com/environment

https://docs.expo.io/versions/latest/expokit/eject/

Summary

If you created an app using create-react-native-app MyApp, ejecting your app gets your app to be the same as if you created your project using react-native init MyApp

aka

create-react-native-app MyApp > make changes to app > eject app

is roughly equivalent to

react-native init MyApp > make changes to app

More Details

What's the difference between create-react-native-app MyApp and react-native init MyApp?

Quick start vs. Full scale development

The philosophy behind create-react-native-app is:

• Minimal "Time to Hello World": Create React Native App should reduce the setup time it takes to try building a mobile app to the absolute minimum, ideally on par with React web development (especially as seen with Create React App).
• Develop on Your Device: It should be easy to develop on a physical device when you want to test how your app feels and responds to inputs.
• One Build Tool: If you just want to get started with React Native, you shouldn't need to install Xcode, Android Studio, NDKs, or mess with environment variables.
• No Lock-In: You can always "eject" to your own build setup if you need to write custom native code or modify how your app is built.

Essentially, create-react-native-app lets you get up and running quickly without having to a do a lot of (or any) configuration. In order to do this, it hides a lot of details from you.

If you want to create a serious app, you need to set up a real development environment. You can do this from scratch by running react-native init <project-name>. If you started with a react native project using create-react-native-app, you can get to this same place by "ejecting" your app

More details from the official documentation about getting started with React Native can be found here.