Limitless App Development with Expo and React Native

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App development is hard, React and Expo make it easy!

It's never been simpler to build and deploy powerful mobile apps with incredible features to both Android and iOS users all over the world.

We’ll discuss building and deploying mobile apps seamlessly from the cloud using EAS, creating powerful dev clients (like browsers but for mobile app development) for testing your app, pushing OTA updates instantly to users, and much more — no native experience required!

Evan Bacon
Evan Bacon
27 min
22 Oct, 2021

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Video Summary and Transcription

Today's Talk discussed building cross-platform apps with React Native and Expo, addressing challenges such as setting up the native runtime and managing dependencies. Expo provides a pre-built runtime, native APIs, fast iteration speed, and integrated cloud services. EAS build simplifies app deployment by handling native code signing and validation. Over-the-air updates allow instant updates to JS and assets. Custom native code can be added using auto-linking and config plugins, and Expo supports both Managed and Bare workflows.

1. Introduction to React Native

Short description:

Today we're talking about building cross-platform apps with React and Expo. React Native allows us to write code once and render to multiple platforms. It uses proper native views for improved performance and allows us to reuse code across platforms. However, there are some challenges, such as setting up the native runtime and managing dependencies. The app's runtime must also be distributed to app stores.

What's up, everyone? I'm Evan Bacon, and today we're going to be talking about building cross-platform apps with React and Expo.

Native app development can be a little bit daunting. So I'm going to be discussing and describing in a way which is comparable to web development.

So first we're going to do a quick recap for anyone who's unfamiliar with React Native. When you want to build an iOS app, you'll use Swift and Objective-C, and when you want to build an Android app, you'll use Java and Kotlin. Now, this often means that you'll have two separate teams which are pretty much working in silos. Obviously, that's less efficient than having one team. But using React Native, we can write React and JavaScript that renders to each platform using the same code base. This is very similar to a mobile browser, which lets you run React DOM code on multiple different platforms, which is by design.

React is very intuitive for building and scaling large front-end applications. Now, the core differences between React DOM and React Native are, instead of drawing our views to Skia, like we would in Chrome, React Native uses proper native views. This means that we can use platform optimizations like smooth scrolling, gestures, and complex animations, which is known to be a weak point in mobile browsers. We can create custom native clients that expose extra native functionality to our app. Think of this like building a browser, but with Bluetooth support added to it. And we can reuse the majority of our application code across multiple different platforms. We have the potential to scale our app to support more platforms in the future. And finally, we can utilize multiple different threads. By default, everything runs in a JavaScript thread, minimizing the amount of business logic that runs on the main UI thread. This is a pretty advanced architecture which you just get for free by simply using React Native. So this is pretty awesome.

Now, React Native, of course, is not without its issues, ranging from mildly annoying to highly annoying. So let's talk about some of them. First is that in order to get a Hello World app running, just Hello World, we need to create a native runtime. This differs from web development where the native runtime is already built ahead of time and downloaded on your computer. That would be Chrome or Safari, the web browsers. And they can just load your JavaScript project inside of them. Second is that dependencies in React Native are much harder to manage than in web development. In React Native, you need to install the native code via NPM, whereas in web development, the native code is already built ahead of time into the browser. And the APIs and native code are designed by W3C, so they're very well thought out and just well constructed. Third is that your app's runtime must be distributed to the App Store or Google Play Store, with a few exceptions for testing of course.

2. Introduction to Expo and React Native Development

Short description:

In this part, we'll discuss the challenges of code signing and upgrading React Native applications. We'll also introduce Expo, a set of tools that solve these issues. Expo provides a pre-built runtime, native APIs, fast iteration speed, and integrated cloud services. We'll cover creating an app, the development cycle, publishing to the store, adding native code, and upgrading the app. To get started, install Expo CLI, create a new project, and use NPM scripts to start on iOS, Android, or web. React Native's development cycle is fast and enjoyable, and it uses primitives to render native views for each platform. Community packages provide additional features.

This means that you must perform code signing for your application, which is complicated and prone to errors. Finally, upgrading your React Native application is quite painful. You need some familiarity with both iOS and Android native development in order to do it, and upgrades happen pretty frequently.

Over the course of this presentation, I'm going to show you how we've solved each one of these issues using a series of tools called Expo. Now, Expo provides many tools that web developers have come to expect, like a reusable pre-built runtime, similar to the browser, or a thoughtful set of features and native APIs that you don't need to really interact with too much, very fast iteration speed, and deeply integrated cloud services that make building and deploying very seamless.

First, we'll talk about creating an app and running it on your devices without having to do any native builds. Then we'll cover the development cycle and adding dependencies, then we'll talk about publishing your app to the store so that you can get it into the hands of users. And finally, we'll talk about adding native code, customizing your client, and easily upgrading your app.

To get started with app development, we just need to install Expo CLI. This is a modern Node.js CLI that helps us interface with the bundler, start up a dev server, and many other development tasks. So we're just going to globally install the package, and then create a new project with Expo init. Here, we'll quickly generate a new project. We don't need any native code to get started. When the project is initialized, we can use NPM scripts in order to start up instantly on iOS Android web, which are the platforms that are supported by Expo by default. Yarn Android starts up the Metro bundler and opens up the project on Android. Yarn iOS opens up the simulator, and Web starts up the web pack dev server, and opens your project in the browser.

Now, Expo in React Natives development cycle is pretty top-notch, even just like for web development. So here, I'll open the app on both iOS and Android, instantly. I don't need to do any native builds for that. Then I'll make a few changes to demonstrate fast refresh, which preserves the React's component state between updates. As you can see, the development cycle is pretty fast and really enjoyable. Unlike React DOM development, React Native uses primitives. So instead of div, you'll use something like view. Instead of image, you'll use image. And instead of span, you'll use text. Each one of these elements then draws to the correct native view for each platform. So on iOS, a view would render to a UI view, and on web, a view would render to a div, and so on and so forth. And finally, these primitives render out to something which generally looks the same across all platforms. React Native only provides a handful of core primitives. The majority of complex features come from community packages.

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