This chapter introduced you to storing data offline in React Native applications. The main reason you would want to store data locally is when the device goes offline and your app can't communicate with a remote API. However, not all applications require API calls and AsyncStorage can be used as a general purpose storage mechanism. You just need to implement the appropriate abstractions around it.

You learned how to detect changes in network state in React Native apps as well. It's important to know when the device has gone offline so that your storage layer doesn't make pointless attempts at network calls. Instead, you can let the user know that the device is offline, and then synchronize the application state when a connection is available.

That wraps up the second part of this book. You've seen how to build React components for the Web, and React components for mobile platforms. At the beginning of this book, I posited that the beauty of React lies in the notion of rendering targets. The declarative programming interface of React never has to change. The underlying mechanisms that translate JSX elements are completely replaceable—in theory, we can render React to anything.

In the final part of this book, I'll talk about state in React applications. State and the policies that govern how it flows through an application can make or break the React architecture.