As the Artsy iOS app grew larger, we started hitting pain points:

We want to support other future platforms such as Android without creating more teams.

We want different business teams to work on the app without disrupting each other.

We want our architecture to evolve in order to increase programmer efficiency.

It took us about a year to start resolving these issues. Ideally, we wanted to find a solution to our architectural issues that would also improve the user experience. Notably we wanted more efficient networking, due to mobile device constraints.

It would have been an easy leap to start using Swift and, as a matter of fact, we do use Swift in parts of our flagship application and entirely in 2 other apps.

However, while Swift is a great language, it’s also just that: another language. It does not do much in terms of new paradigms that solved our architectural needs, it does not help in terms of cross-platform - as most of our code is building views and thus very framework specific, and it did not really offer anything in terms of more efficient network data fetching.

We've seen that the web teams integrate React in their projects with really great results. We've been paying attention to React Native since it came out; the solutions provided by the React ecosystem ticked all of our boxes.

Six months ago we took the plunge, and last month we formalized that this is the direction we want to go.

Cons

So you decided to read the full post and the first thing you got confronted with is a list of cons… boo. Let’s just get these out of the way first, it will only get better afterwards.

Dependencies, dependencies, dependencies, both in libraries and tooling. Once you open this can, you’ll have worms everywhere in no time; 593 packages to be exactly, at the time of writing, for a new React Native project. Good luck maintaining that. Having created a dependency manager, I’m not afraid of some dependencies and don’t subscribe to NIH, but the JavaScript community has gone way overboard for my taste. If, like me, you subscribe to the idea that dependencies are part of your application and you want to be able to know what packages are being pulled in so you can maintain them, then you probably won’t like this aspect very much either. I’m not quite sure yet how I feel about this in the long run and what we can do about it, short of trying to get the maintainers of the packages we directly depend on to accept changes that simplify their dependency graphs.

As is often the case, error reporting does not always receive the attention it should get. With the amount of tools and libs that make up the full stack you need to work with, this lack in attention to failure resolution can quickly cascade into deep rabbit holes.

React Native is still very young and fast moving. If you don’t like living on the edge (i.e. lots of updating and dealing with breaking changes) nor have an interest in shaping an unfinished framework, this currently is not for you.

All Facebook open-source code is made to solve the problems that Facebook has first, thus with young projects you may well need to put in a bunch of time to make it work for your problem set. React Native provides a lot of basic view building blocks, but you do lose a lot that you would get with UIKit for free, e.g. UICollectionView . However, it is important to note that this is only a heads-up for those that might think they can solve any problem out-of-the-box; in terms of open-source code I prefer code used in production over other code any day.

There are currently many more people trying to get help, with often arguably simple questions in the context of iOS development, compared to those willing to spend time on answering questions. Most forums I’ve seen suffer from the tragedy of the commons problem, which can be a real problem if you have incidental framework specific questions, but jumping to React Native probably is a complete disaster if you know very little about iOS development yet. If you’re not already knowledgeable about iOS development, are not motivated to put in the time to learn about the platform specific details, and think making rich iOS applications with React Native will be a breeze, you’ll come home from a very cold fair indeed. While you can definitely make applications that way, in my experience those often end up not feeling like proper citizens of the platform they inhibit.

Due to React Natives immaturity, you will not be able to find nuanced post-mortems on the subject. The project is only at the beginning of the hype cycle, meaning there is a lot to gain in writing about how great it is, but less incentive to discuss where it doesn't work out well.

Pros, why we wanted to use React Native

From the React website: React will efficiently update and render just the right components when your data changes. Build encapsulated components that manage their own state, then compose them to make complex UIs. The functional model that React introduces that allows you to reason about the state of your views in much simpler ways has for us been a welcome change that should make it much easier to write decoupled code going forward. I’m by no means a functional programming purist, nor do I really care for being one. I found the React/React Native communities to be very welcome to functional enthusiasts and pragmatists alike, a healthy mix that I find leads to more productive outcomes.

Relay. From its website: Queries live next to the views that rely on them, so you can easily reason about your app. Relay aggregates queries into efficient network requests to fetch only what you need. The clarity this brings to the view codebase - coupled with its smart caching, networking is just ground-breaking. No more multiple levels of model code in your application that you need to trace, just a single file with the view component and the data it needs. Neat. We do still have ‘view models’, however, those now pretty much all live in our GraphQL service. The added benefit here is that we share that model logic with Artsy’s other (web) clients.

“Learn once, write anywhere.” is the neo-cross-platform slogan deployed by React, which is a play on the tried “Write once, run anywhere.” slogan of yesteryear. The difference being that you can use the same paradigms to create products on various platforms, rather than pure code-reuse. While we haven’t put this to the test yet at Artsy, we do plan to team up people across platforms to implement single features on each respective platform, rather than having multiple people implement the same feature on their own. The hope is that this will lead to better understanding of features and thus the implementations thereof, while still taking each platform’s unique nature into account. The added benefit would be that people learn to understand and appreciate those unique platform traits, thus making them more well-rounded engineers. In the long run, we hope to extend this way of working as we start work on a React Native Android client.

While Auto Layout is a great step up from manual frame calculation, most of our views don’t need the granularity that Auto Layout offers. React Native ditches Auto Layout and instead uses flexbox for its layout. While my head has never been able to fully wrap around classic CSS, I find that flexbox is an abstraction that nicely fits most of our needs. I can definitely imagine situations in which more granularity would be required, however, in those cases we can always decide to ‘drop down’ to native view code, so I don’t really worry too much about that.

Layout calculations are performed on a background thread, the so-called ‘shadow’ thread. This can make a big difference when e.g. scrolling through a large complex list view. Granted, you can do this with UIView , but the pattern is not as ingrained in UIKit thus usually leading to more holistic replacements such as AsyncDisplayKit.

Great separation of declarative view layout (JS, single-threaded) and technical details (native code, multi-threaded). Because of the hard constraint of having a JS/native bridge, there really is no way to take shortcuts (e.g. spaghetti code) that in the long run would only lead to technical debt. Constraints are great.

Because there’s very little code that needs to be compiled and how the isolated component nature of React makes it it very easy to reload code in-process, development velocity lies much higher than with your typical native UIKit-based development.

While, as mentioned above, there are definitely issues with the tooling and libs, on the flip-side it is all open-source software and you can (officially) dive in and figure it out, unlike e.g. Xcode and UIKit. (Granted, you still need to deal with these when using React Native, but it can be kept to a minimal surface.)

Because React Native is still young, fast moving, and open-source, this is a great time to help shape the framework you’d want to use.

Things we learned

When we started out with React Native, I didn't want to have to re-write our application in order to take advantage of the technology. To address this I worked within our existing application structure. We consider the App to be a browser of native and web view controllers. So, we added routes to our SwitchBoard for view controllers which are created in React Native. To the rest of the app, there is no difference between a Swift view controller, or one with React Native inside.

All of the React Native code is kept in a completely separate repo, Emission, which when deployed generates a minified version of the JavaScript. This means to build the Artsy iOS app you do not need to have a JavaScript development environment.

We reused a lot of our existing native views, starting with loading indicators and native switch views.

We used new native classes to improve integration, for example the <OpaqueImageView> component is a native UIImageView subclass that works with our application-wide SDWebImage image cache.

Conclusion

To really shine with React Native, you need native experience. JavaScript has not eaten everything yet. However, you don't need a team of native experts. For example, we expect to be able to get quite far with Android support based on our work in React Native, but to make it amazing, we will need someone with history and context in the space.

This frees up our engineers to widen their T-shaped skills, and to help remove the idea that the mobile team has to be a completely separate team with foreign tools and ideas.

This is only the tip of the iceberg for our writings about React Native. Follow @ArtsyOpenSource to stay up to date.