Hello Reason React Native

2019-06-17 | By @MoOx

Today is a big day for the ReasonML community as we are releasing the fruits of a long effort started about 4 months ago.

As more and more people were starting to use ReasonML on production apps using React Native, we wanted to make the BuckleScript bindings for React Native, known has bs-react-native, more accessible. This would have involved several breaking changes in order to simplify some APIs that have been designed with a high level of security in mind, but at some costs. The cost of being harder to start with (for newcomers to ReasonML) as well as the cost in terms of code size and performance.

While some of us were thinking about some simplifications, some others, involved in Reason React incoming changes, directly started a new approach for this bindings, following the zero-cost approach offered by reason-react 0.7.0.

CCA started this effort on what is now know as the new reason-react-native bindings, that eliminates a huge part of the additional JavaScript code produced by the bindings.


By zero-cost, we means zero additional cost. The JavaScript code BuckleScript produces using this bindings will most of the time directly hit React Native JavaScript code without creating an unnecessary abstraction above it 🙌.

Here are some random examples:

Some modules are even empty or with some minor require() that can be themselves almost empty and easily removed by some JavaScript bundlers.

How cool is that?

But why reason-react-native ?

bs-react-native already had multiple breaking changes in the past and we didn't really want to offer a poor experience by creating a new release with tons of changes that won't be easy to codemod (or would require much more work from us).

On top of that, reason-react latest release already added an important breaking change with JSX 3.

That's why we had this idea about offering an easy and smooth transition by offering 2 packages to say goodbye to bs-react-native without pain.


bs-react-native-jsx3-compat (0.11.1)


reason-react-native (0.60.0)

Wait, what is bs-react-native-jsx3-compat ?

bs-react-native is using JSX 2 so in order to use it with JSX 3 we would have to create an additional layer on top of the current bindings to offer both JSX 2 and 3 bindings. And since we wanted to do away with some current APIs of bs-react-native we started to think about a new approach.

We knew that we wanted to:


offer to bs-react-native users a migration plan, so they can start very easily to use JSX 3 and new reason-react (so they can use hooks),


offer new reason-react-native bindings, more accessible and with a zero cost approach.


offer a smooth transition between these two packages so people can slowly upgrade their codebase without having to make an insane PR that switches from one to the other.

We don't want your co-workers to hate you with a PR that comes directly from hell 😅.

That's where we thought about offering bs-react-native-jsx3-compat. It's a package that has the same APIs bs-react-native has but that uses reason-react-native under the hood.

This means you will have to make a migration from JSX 2 to 3. That's the only thing you will have to do, then with a single change from bs-react-native with bs-react-native-jsx3-compat in your bs-dependencies you will be ready to use hooks and directly benefit of (almost) zero-cost bindings!

And since we care about you and don't want you to upgrade from JSX 2 to 3 by hand, we got you covered with a script made with love to help you with that.



bs-react-native has now entered a frozen state and won't receive any upgrade


bs-react-native-jsx3-compat allows you to use existing code based on bs-react-native with reason-react 0.7.0 and JSX 3


reason-react-native package contains the new bindings for React Native, that offers more accessible APIs and that is almost zero-cost


This required effort has been keeping us busy for weeks and wouldn't have been possible without the following people:


CCA team and especially @cknitt for leading us to the right direction for the new zero-cost bindings and all the contributions that come with this move


@sgny for all his contributions to the new bindings


@MoOx for leading the effort, the compat layer and the new website you are seeing here


@bloodyowl for his magical reason-react-compat layer and the alternate JSX 3 upgrade path that goes with it


all the people that helped us on Discord and GitHub in various code reviews and improvements like the react native template (thanks @dawee)

What's next?

Now that reason-react-native is ready to be used and that our migration plan is usable, we will probably be focused on documentation as lots of APIs and Components need to be documented. We really want to offer the best developer experience possible and that's definitely part of it.

👉Now it's time for you to check our Getting Started with Reason React Native documentation