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Stand alone, low configuration ClojureScript tooling for React Native. All features are provided as a simple set of defaults over the standard ClojureScript compiler.

Releases & Dependency Information

io.vouch/krell {:mvn/version "0.5.3"}

Why Krell?

There are two other relatively mature ClojureScript tools for React Native, re-natal and shadow-cljs. re-natal is oldest and likely most widely used. Unfortunately, re-natal is Leiningen-centric and has some historical design decisions that lead to a stateful CLI API. Still, it is a direct inspiration for Krell, and re-natal solved many tricky edge-cases early on. shadow-cljs also offers react-native integration, but provides that as part of a full featured package rather than an à la carte tool.

Krell fills the gap by providing a standalone tool with few dependencies. It does only one thing - extend the standard ClojureScript compiler to make developing React Native simpler (and easier).

It does not attempt to paper over the React Native CLI workflow at all. Krell just provides minimal sensible defaults for development and production and allows you to switch between these defaults via the familiar ClojureScript :optimizations settings.

With little configuration beyond typical ClojureScript web config, you get a React Native REPL-based workflow. Because Krell uses the ClojureScript compiler to index node_modules, you can idiomatically require anything you've installed via yarn or npm just like any ClojureScript library.

If you specify a higher optimization setting like :simple or :advanced, Krell generates a single file output without the REPL dependencies.


  • Node >= 10.16.0
  • Latest release of ClojureScript
  • Java SDK 8+

Using React Native >= 0.60 is highly recommended as autolinking simplifies usage greatly. If you must use an older version of React Native refer to the documentation for the REPL support dependencies: react-native-tcp-socket.

Install REPL Dependencies

Install the REPL support dependencies:

clj -M -m cljs.main --install-deps

If this fails try:

clj -M -m cljs.main -co "{:deps-cmd \"yarn\"}" --install-deps

Switch into the ios directory of your project and run pod install.


First build your project:

clj -M -m krell.main -v -co build.edn -c

Run your React Native project and verify that it works.

You can start a REPL and connect to the running app at any time:

clj -M -m krell.main -co build.edn -r

You can of course combine these steps just as with plain cljs.main.

clj -M -m krell.main -co build.edn -c -r

Assets & Arbitrary Node Library Requires

Krell supports arbitrary js/require of assets and Node.js dependencies. The asset support is intended to align with React Native's own documentation - you must use static relative paths. The additional support for Node.js dependencies is useful when transitioning away from re-natal to Krell.

It's important to note that adding a new asset or new Node library currently requires recompiling the project.

Other than that there are no other limitations. The handling of js/require is implemented as an analyzer pass so if you want to create macros to generate asset requires, that will work.

Extending Krell

Integrating with tools like Expo, and Storybook.js require providing a custom index.js file. This can be provided by one of two ways - either via the --index-js command line flag or by providing a file called krell_index.js on the classpath. The later method opens the door to extending Krell to other targets without requiring any configuration or wrapping of Krell at all.

Multiple App Instance Development

Sometimes it's necessary run multiple instances of the same application during development - i.e. a chat/messaging application. When Krell starts up it logs the device ID, for example:

Krell sez howdy, Device ID: iPhone12,3

You can use this device ID to assign a specific Krell port in your app.json, for example:

  "name": "MyAwesomeProject",
  "displayName": "My Awesome Project",
  "krellPortMap": {
    "iPhone12,3": 5002

Then you can connect to it like so:

clj -M -m krell.main -co build.edn -p 5002 -r

You should only have one hotloading REPL. You can disable hot reloading like so:

clj -M -m krell.main -co build.edn -p 5002 -rc false -r


See the Reagent example tutorial in the wiki.

Tooling Integration

See the wiki.


Currently Krell is only taking bug reports. If you find a bug or would like to see an enhancement that aligns with the following design principles please file a Github issue!

Design Principles

  • No ClojureScript React library integration templating. The documentation should make it pretty clear how to integrate with any particular ClojureScript React library.

  • Basic React Native only, we're not interested in Expo or any other similar tooling


Copyright (c) Vouch, Inc. All rights reserved. The use and
distribution terms for this software are covered by the Eclipse
Public License 1.0 (
which can be found in the file epl-v10.html at the root of this
distribution. By using this software in any fashion, you are
agreeing to be bound by the terms of this license. You must
not remove this notice, or any other, from this software.