shadow-cljs provides everything you need to compile your ClojureScript code with a focus on simplicity and ease of use.

shadow-cljs

ClojureScript compilation made easy!

Configurations

For a browser app, create a shadow-cljs.edn file like:

{:source-paths ["src"]
 :dependencies [[reagent "0.8.1"]]
 :builds {:app {:target :browser
                :output-dir "public/js"
                :asset-path "/js"
                :modules {:main {:init-fn app.main/main!}}}}}

which means:

{:source-paths ["src"] ; where you put source files

 :dependencies [[reagent "0.8.1"]] ; ClojureScript dependencies

        ; "app" is the build-id, in running "shadow-cljs compile app"
 :builds {:app {:target :browser ; compile code that loads in a browser
                :output-dir "public/js"
                :asset-path "/js" ; assets loaded from index.html are based on path "/js"

                        ; "main.js" is the name for the bundle entry
                :modules {:main {:init-fn app.main/main!}}}}}
                               ; function app.main.main! is called when page loads

Use :target :node-script for compiling in Node.js and there are also more targets to try.

To publish a ClojureScript package with dependencies from npm, add a dep.cljs file. shadow-cljs will read it and install those npm modules.

CLI tools

Some useful shadow-cljs commands during development are:

# compile a build once and exit
shadow-cljs compile app

# compile and watch
shadow-cljs watch app

# connect to REPL for the build (available while watch is running)
shadow-cljs cljs-repl app

# connect to standalone node repl
shadow-cljs node-repl

Running a release build optimized for production use.

shadow-cljs release app

Find out more commands in the docs.

Using modules from npm

With shadow-cljs, most npm modules for browser can be imported with modules installed locally.

(ns app.main
  (:require ["md5" :as md5]
            ["fs" :as fs]))

(println (md5 "text"))

(fs/readFileSync "deps.den" "utf8")

Lifecycle Hooks

You can configure the compiler to run functions just before hot code reload brings in updated code, and just after. These are useful for stopping/starting things that would otherwise close over old code.

(ns my.app)

(defn ^:dev/before-load stop []
  (js/console.log "stop"))

(defn ^:dev/after-load start []
  (js/console.log "start"))

Find more configs in user manual.

Non-code resources

There are various use-cases where you’d want to use a static resource as part of the compilation of your source files. shadow-cljs provides a macro shadow.resource/inline for loading files from inside classpaths:

(ns demo.app
  (:require [shadow.resource :as rc]))

(def docs (rc/inline "./docs.md")) ; docs is the string content of the file

; also like:
; (def docs (rc/inline "demo/docs.md"))

This will resolve the ./docs.md file relative to the current namespace, which means it will end up including demo/docs.md from somewhere on the classpath.

Long-term caching

By setting in :module-hash-names field you may tell shadow-cljs to add MD5 hash in the filenames generated. It's a trivial feature in Webpack and now it's a one-liner config in ClojureScript. Meanwhile the assets.edn file can be emitted for indexing js files in HTML.

{:source-paths ["src"]
 :dependencies [[mvc-works/hsl "0.1.2"]]
 :builds {:browser {:target :browser
                    :output-dir "target/browser"
                    :modules {:main {:init-fn app.main/main!}}

                    :release {:output-dir "dist/"
                              :module-hash-names 8
                              :build-options {:manifest-name "assets.edn"}}}}}

After compilation, two files will be generated in dist/ with names:

=>> l dist/
assets.edn        main.9683CD2F.js

Embedding in the JS Ecosystem — The :npm-module and :esm Target

There is an additional target that is intended to help you use shadow-cljs as part of a project and provide seamless integration with existing JS tools (eg. webpack, browserify, babel, create-react-app, …) with as little configuration as possible.

Sample source for src/main/demo/foo.cljs

(ns demo.foo)

(defn hello [who]
  (str "Hello, " who "!"))

Compile code to `:npm-module` target

{
 ; ...
 :builds {:npm {:target :npm-module
                ; ...
                }}}

The generated exports will be named shadow-cljs/ with the CLJS namespace.

$ node
> var x = require("shadow-cljs/demo.foo");
undefined
> x.hello("JS")
'Hello, JS!'

It is now also possible to generate “almost” standards-complient ESM output. It says “almost” because it is technically cheating in development. release builds are fully :advanced optimized and compliant as they don’t leak any globals or do any other kinds of eval tricks.

The generated code can be loaded as a module. Find out more about `:esm` target.

<script type="module" src="/js/demo.js"></script>

Other features

There are more features in shadow-cljs, such as:

Dynamic code loading

Testing

Editor Integration

Read the User Guide to learn about all the features.

Getting started

Here are some configurations you can start with:

compile a browser app

compile a Node.js script

compile with optimizations

emits multiple bundles and load on need

emits code in CommonJS syntax

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