After years of native mobile development, we’ve decided to go full steam ahead building all of our new mobile apps using React Native. As I’ll explain, that decision doesn’t come lightly.

Each quarter, the majority of buyers purchase on mobile (with 71% of our buyers purchasing on mobile in Q3 of last year). Black Friday and Cyber Monday (together, BFCM) are the busiest time of year for our merchants, and buying activity during those days is a bellwether. During this year’s BFCM, Shopify merchants saw another 3% increase in purchases on mobile, an average of 69% of sales.

So why the switch to React Native? And why now? How does this fit in with our native mobile development? It’s a complicated answer that’s best served with a little background.

Mobile at Shopify Pre-2019

We have an engineering culture at Shopify of making specific early technology bets that help us move fast.

On the whole, we prefer to have few technologies as a foundation for engineering. This provides us multiple points of leverage:

• we build extremely specific expertise in a small set of deep technologies (we often become core contributors)
• every technology choice has quirks, but we learn them intimately
• those outside of the initial team contribute, transfer and maintain code written by others
• new people are onboarded more quickly.

At the same time, there are always new technologies emerging that provide us with an opportunity for a step change in productivity or capability. We experiment a lot for the opportunity to unlock improvements that are an order of magnitude improvement—but ultimately, we adopt few of these for our core engineering.

When we do adopt these early languages or frameworks, we make a calculated bet. And instead of shying away from the risk, we meticulously research, explore and evaluate such risks based on our unique set of conditions. As is often within risky areas, the unexplored opportunities are hidden. We instead think about how we can mitigate that risk:

• what if a technology stops being supported by the core team?
• what if we run into a bug we can’t fix?
• what if the product goes in a direction against our interests?

Ruby on Rails was a nascent and obscure framework when Tobi (our CEO) first got involved as a core contributor in 2004. For years, Ruby on Rails has been seen as a non-serious, non-performant language choice. But that early bet gave Shopify the momentum to outperform the competition even though it was not a popular technology choice. By using Ruby on Rails, the team was able to build faster and attract a different set of talent by using something more modern and with a higher level of abstraction than traditional programming languages and frameworks. Paul Graham talks about his decision to use Lisp in building Viaweb to similar effect and 6 of the 10 most valuable Y Combinator companies today all use Ruby on Rails (even though again, it still remains largely unpopular). As a contrast, none of the Top 10 most valuable Y Combinator companies use Java; largely considered the battle tested enterprise language.

Similarly two years ago, Shopify decided to make the jump to Google Cloud. Again, a scary proposition for the 3rd largest US Retail eCommerce site in 2019—to do a cloud migration away from our own data centers, but to also pick an early cloud contender. We saw the technology arc of value creation moving us to focusing on what we’re good at—enabling entrepreneurship and letting others (in this case Google Cloud) focus on the undifferentiated heavy lifting of maintaining physical hardware, power, security, the operating system updates, etc.

What is React Native?

In 2015, Facebook announced and open sourced React Native; it was already being used internally for their mobile engineering. React Native is a framework for building native mobile apps using React. This means you can use a best-in-class JavaScript library (React) to build your native mobile user interfaces.

At Shopify, the idea had its skeptics at the time (and still does), but many saw its promise. At the company’s next Hackdays the entire company spent time on React Native. While the early team saw many benefits, they decided that we couldn’t ship an app we’d be proud of using React Native in 2015. For the most part, this had to do with performance and the absence of first-class Android support. What we did learn was that we liked the Reactive programming model and GraphQL. Also, we built and open-sourced a functional renderer for iOS after working with React Native. We adopted these technologies in 2015 for our native mobile stack, but not React Native for mobile development en masse. The Globe and Mail documented our aspirations in a comprehensive story about the first version of our mobile apps.

Until now, the standard for all mobile development at Shopify was native mobile development. We built mobile tooling and foundations teams focused on iOS and Android helping accelerate our development efforts. While these teams and the resulting applications were all successful, there was a suspicion that we could be more effective as a team if we could:

• bring the power of JavaScript and the web to mobile
• adopt a reactive programming model across all client-side applications
• consolidate our iOS and Android development onto a single stack.

How React Native Works

React Native provides a way to build native cross platform mobile apps using JavaScript. React Native is similar to React in that it allows developers to create declarative user interfaces in JavaScript, for which it internally creates a hierarchy tree of UI elements or in React terminology a virtual DOM. Whereas the output of ReactJS targets a browser, React Native translates the virtual DOM into mobile native views using platform native bindings that interface with application logic in JavaScript. For our purposes, the target platforms are Android and iOS, but community driven effort have brought React Native to other platforms such as Windows, macOS and Apple tvOS.

When Will We Not Default to Using React Native?

There are situations where React Native would not be the default option for building a mobile app at Shopify. For example, if we have a requirement of:

• deploying on older hardware (CPU <1.5GHz)
• extensive processing
• ultra-high performance
• many background threads.

Reminder: Low-level libraries including many open sourced SDKs will remain purely native. And we can always create our own native modules when we need to be close to the metal.

Why Move to React Native Now?

There were 3 main reasons now is a great time to take this stance:

1. we learned from our acquisition of Tictail (a mobile first company that focused 100% on React Native) in 2018 how far React Native has come and made 3 deep product investments in 2019
2. Shopify uses React extensively on the web and that know-how is now transferable to mobile
3. we see the performance curve bending upwards (think what’s now possible in Google Docs vs. desktop Microsoft Office) and we can long-term invest in React Native like we do in Ruby, Rails, Kubernetes and Rich Media.

Mobile at Shopify in 2019

We have many mobile surfaces at Shopify for buyers and merchants to interact, both over the web and with our mobile apps. We spent time over the last year experimenting with React Native with three separate teams over three apps: Arrive, Point of Sale, and Compass.

From our experiments we learned that:

• in rewriting the Arrive app in React Native, the team felt that they were twice as productive than using native development—even just on one mobile platform
• testing our Point of Sale app on low-power configurations of Android hardware let us set a lower CPU threshold than previously imagined (1.5GHz vs. 2GHz)
• we estimated ~80% code sharing between iOS and Android, and were surprised by the extremely high-levels in practice—95% (Arrive) and 99% (Compass)

As an aside, even though we’re making the decision to build all new apps using React Native, that doesn’t mean we’ll automatically start rewriting our old apps in React Native.

Arrive

At the end of 2018, we decided to rewrite one of our most popular consumer apps, Arrive (which is now Shop app) in React Native. Arrive is no slouch, it’s a highly rated, high performing app that has millions of downloads on iOS. It was a good candidate because we didn’t have an Android version. Our efforts would help us reach all of the Android users who were clamoring for Arrive. It’s now React Native on both iOS and Android and shares 95% of the same code. We’ll do a deep dive into Arrive in a future blog post.

So far this rewrite resulted in:

• less crashes on iOS than our native iOS app
• an Android version launched
• team composed of mobile + non-mobile developers.

The team also came up with this cool way to instantly test work-in-progress pull requests. You simply scan a QR code from an automated GitHub comment on your phone and the JavaScript bundle is updated in your app and you’re now running the latest code from that pull request. JML, our CTO, shared the process on Twitter recently.

Point of Sale

At the beginning of 2019, we did a 6-week experiment on our flagship Point of Sale (POS) app to see if it would be a good candidate for a rewrite in React Native. We learned a lot, including that our retail merchants expect almost 2x the responsiveness in our POS due to the muscle memory of using our app while also talking to customers.

In order to best serve our retail merchants and learn about React Native in a physical retail setting, we decided to build out the new POS natively for iOS and use React Native for Android.

We went ahead with 2 teams for the following reasons:

1. we already had a team ramped up with iOS expertise, including many of the folks that built the original POS apps
2. we wanted to be able to benchmark our React Native engineering velocity as well as app performance against the gold standard which is native iOS
3. to meet the high performance requirements of our merchants, we felt that we’d need all of the Facebook re-architecture updates to React Native before launch (as it turns out, they weren’t critical to our performance use cases). Having two teams on two platforms, de-risked our ability to launch.

We announced a complete rewrite of POS at Unite 2019. Look for both the native iOS and React Native Android apps to launch in 2020!

Compass

The Start team at Shopify is tasked with helping folks new to entrepreneurship. Before the company wide decision to write all mobile apps in React Native came about, the team did a deep dive into Native, Flutter and React Native as possible technology choices. They chose React Native and had iOS and Android apps live in the app stores.

The first versions of Compass, which is now Shopify Learn, were launched within 3 months with ~99% of the code shared between iOS and Android. 

Mobile at Shopify 2020+

We have lots in store for 2020.

Will we rewrite our native apps? No. That’s a decision each app team makes independently

Will we continue to hire native engineers? Yes, LOTS!

We want to contribute to core React Native, build platform specific components, and continue to understand the subtleness of each of the platforms. This requires deep native expertise. Does this sound like you?

Partnering and Open Source

We believe that building software is a team sport. We have a commitment to the open web, open source and open standards.

We’re sponsoring Software Mansion and Krzysztof Magiera (co-founder of React Native for Android) in their open source efforts around React Native.

We’re working with William Candillon (host of Can It Be Done in React Native) for architecture reviews and performance work.

We’ll be partnering closely with the React Native team at Facebook on automation, 3rd party libraries and stewardship of some modules via Lean Core.

We are working with Discord to accelerate the open sourcing of FastList for React Native (a library which only renders list items that are in the viewport) and optimizing for Android.

Developer Tooling and Foundations for React Native

When you make a bet and go deep into a technology, you want to gain maximum leverage from that choice. In order for us to build fast and get the most leverage, we have two types of teams that help the rest of Shopify build quickly. The first is a tooling team that helps with engineering setup, integration and deployment. The second is a foundations team that focuses on SDKs, code reuse and open source. We’ve already begun spinning up both of these teams in 2020 to focus on React Native.

Our popular Shopify Ping app (now called Shopify Inbox) which has enabled hundreds of thousands of customer conversations is currently only iOS. In 2020, we’ll be building the Android version using React Native out of our San Francisco office and we’re hiring.

In 2019, Twitter released their desktop and mobile web apps using something called React Native Web. While this might seem confusing, it allows you to use the same React Native stack for your web app as well. Facebook promptly hired Nicolas Gallagher as a result, the lead engineer on the project. At Shopify we’ll be doing some React Native Web experiments in 2020.

Learn More About React Native at Shopify

• A First Look at Reanimated 2
• Building Arrive's Confetti in React Native with Reanimated
• Tophatting in React Native
• Creating Native Components That Accept React Native Subviews
• Management of Native Code and React Native at Shopify

Join Us

Shopify is always hiring sharp folks in all disciplines. Given our particular stack (Ruby on Rails/React/React Native) we’ve always invested in people even if they don’t have this particular set of experiences coming in to Shopify. In mobile engineering (btw, I love this video about engineering opinions) we’ll continue to write mobile native code and hire native engineers (iOS and Android).

Farhan Thawar is VP Engineering for Channels and Mobile at Shopify
Twitter: @fnthawar