TL;DR: Here’s a way to share application logic between a React Web app and a React Native app, while keeping the individual component rendering unique to each platform. The example app can be found on GitHub.

The app

React Native React Web

The app itself is a very simple Hello World (ish) app. Not only does it show “Hello World”… but when you click (or tap) it… it changes from red to blue! woah!

Motivation

Writing React apps is awesome for both web and mobile… so why not share code between your two implementations?

Let me just say right off the bat that React Native/React wasn’t designed to be a “write once, run everywhere” framework. Facebook constantly calls it a “learn once, write everywhere” framework - the idea being that you tailor your implementation to the platform you’re writing for. That said, you can still share a great deal of logic between your applications.

In this post I’ll be discussing how you can take a more “middle of the road” approach between these mentalities. We’ll be sharing all the application logic while keeping the rendering code specific to each platform.

We’ll be assuming some knowledge of React, React Native, and Redux.

Initial Setup + Directory Overview

First we need to initialize our project. We’re going to follow the steps dictated in Facebook’s getting started guide:

$ npm install -g react-native-cli $ react-native init ReactNativeWebHelloWorld

We now have a directory that looks like:

ReactNativeWebHelloWorld |-- android |-- ios |-- node_modules |-- .flowconfig |-- .gitignore |-- .watchmanconfig |-- index.android.js |-- index.ios.js +-- package.json

This contains all the files we’ll need for both our iOS and Android app. We now create the following directories and files to configure and run our Web app:

ReactNativeWebHelloWorld +-- web |-- public | +-- index.html +-- webpack |-- web.dev.config.js +-- web.prod.config.js

The contents of index.html , web.dev.config.js , and web.prod.config.js can all be found in the GitHub repo - we’ll dive into them more later (but if you want to click on them now, by all means… do it!).

After our directory structure is configured, we install the dependencies we’ll be needing for the application:

$ npm install --save babel babel-polyfill ... $ npm install --save-dev autoprefixer babel-core ...

For a full list of dependencies, check out the package.json .

For the final bit of set up (woo!), we initialize all of the files for our actual application. We’ll be making a fairly “traditional” React/Redux app:

ReactNativeWebHelloWorld +-- app |-- actions |-- constants |-- reducers |-- store |-- native | |-- components | |-- containers | +-- style +-- web |-- components |-- containers +-- style

At this point it should be getting fairly clear what’s going on. We have three different entry points for our three different apps: index.ios.js , index.android.js , and app/web/index.js . The iOS and Android entry points load the components and containers from app/native , and the web entry point loads components and containers from app/web . This brings us to our…

Application Code Structure

I’m not going to go through every single file and that file’s place and purpose in this whole mess, but I am going to point out some key differences between native and web.

Let’s look at the app entry points, shall we? index.ios.js looks like:

import React , { Component , AppRegistry } from 'react-native' ; import Root from './app/native/containers/Root' ; import configureStore from './app/store/configureStore.prod.js' ; const store = configureStore (); class ReactNativeHelloWorld extends Component { render () { return ( < Root store = { store } / > ); } } AppRegistry . registerComponent ( 'ReactNativeWebHelloWorld' , () => ReactNativeHelloWorld );

And app/web/index.js …

import React from 'react' ; import { render } from 'react-dom' ; import Root from './containers/Root' ; import configureStore from '../store/configureStore' ; // load our css require ( './styles/style.less' ); const store = configureStore (); const rootElement = document . getElementById ( 'root' ); render ( < Root store = { store } />, rootElement ) ;

Ok, so what are the differences that we care about?

The main thing to notice is how the top-level component renders itself into either the page or the app. In native-land, we have to explicitly define a top-level react component that registers itself with the app registry, whereas in web-town we can, using ReactDom , render our Root directly into our root element.

WHAT DOES THAT MEAN!?

Basically, React Native and React Web have different ways of instantiating the top-level component.

It’s these differences that require us to keep the rendering logic unique to each platform.

Let’s also examine the HelloWorld component’s render method in both cases. In Native, it looks like:

render () { const { onPress , color } = this . props ; const style = StyleSheet . create ({ helloWorld : { color : color , textAlign : 'center' } }); return ( < View > < Text onPress = { onPress } style = { style . helloWorld } > Hello World < /Text > < /View > ); }

And for web, it looks like:

render () { const { onClick , color } = this . props ; return ( < div className = "hello-world" onClick = { onClick } style = { { color : color } } > Hello World < /div > ); }

This reinforces that point in bold up there about why we need to keep the rendering logic unique to each platform. React native deals in <View> s and <Text> s whereas the web deals with <div> s and <span> s. Not only that, but both the event system and style system are different.

But let’s look at what’s shared between them for a second…

When instantiating the HelloWorld component, app/native/containers/App.js defines…

< HelloWorld onPress = {() => dispatch ( toggleColor ())} color = { color } / >

and app/web/containers/App.js defines…

< HelloWorld onClick = {() => dispatch ( toggleColor ())} color = { color } / >

Both dispatch methods are injected via react-redux , and toggleColor is imported from the same actions file. ONLY THE RENDERING IS DIFFERENT! THE APPLICATION LOGIC IS SHARED! It’s a leap day miracle!

Rather than go through each individual difference and similarity one by one (as that would result in a novel’s worth of explanation) we’re going to move on to the scripts defined in package.json that allow you to build and run this bad boy…

Configured Scripts

Running in dev/production

There are 8 defined scripts in package.json:

start ios-bundle ios-dev-bundle android-bundle android-dev-bundle web-bundle web-dev

start

start is used when running/bundling the native application. When you open either the xcode project or the android studio project and hit “run”, it kicks off a node server via the start command. Every time you make a JavaScript change, instead of needing to rebuild and recompile your application, you simply refresh the app and the changes are magically there. As this is not a React Native guide I will not be going into more detail than that - further information can be found on Facebook’s React Native Getting Started guide.

bundlin

For ios-bundle , ios-dev-bundle , android-bundle , and android-dev-bundle , the script builds the JavaScript bundle (either minified or not-minified depending on the presence of dev or not), and places it where the corresponding project expects it to be for running locally on your device. Again, you can find more info on running on your device on Facebook’s React Native Getting Started.

web town

web-dev kicks off a webpack server on port 3001, it utilizes hot reloading with some redux-time-machine-magic to have a crazy awesome dev experience where you can rewind and revert actions in your application.

web-bundle creates a minified JavaScript bundle (that also houses the minified css) and places it next to the index.html in web/public that you can serve with any static file server.

clear-cache

Every now and then, when React Native is doing it’s thing, you’ll swear that you’ve changed something, but alas it is still causing your app to break! oh noes! what do we do!

npm run clear-cache

Further Configuration

Webpack sets the PLATFORM_ENV environment variable to be web . You can use this check to conditionally load different files depending on if you’re building your native or web app. For example - you can abstract out the difference between local storage mechanisms.

What does this get you?

Well, first of all, this was pretty fun to set up. Often it’s good to do something in the pure spirit of education. But if that’s not enough for ya, consider any bug that’s caused in the action/reducer/request layer of your app

fixing it once will abolish the bug in both your web and mobile versions.

It also allows for pretty rapid development on both platforms. I was able to get one of my react/redux apps running on mobile feature-complete after about two days of effort.

phew!

Thanks for stickin’ with me, through this one. I know it was alot.