Nodifying Clojure

May 18, 2013


In this post ill cover how to integrate ClojureScript (cljs in short) with nodejs, the use case I was trying to solve was to write hubot integration script with a product Im working on.

Hubot scripts are written using Coffeescript but iv really missed the power of Clojure under my finger tips so iv decided to write a nodejs library with all the main logic in cljs. I wanted to have a full development stack with build, dependency management and testing support.

A key point to understand is that a cljs/node project is living on dual platforms at once, it has dependencies rooted in its nodejs package.json file and some in its cljs project.clj not to mention two build procedures.

Setting up:

The tool chain required in setting up a project include:

  • lein the Clojure build tool we will be using lein-cljsbuild plugin in order to compile our cljs code.
  • npm which is the nodejs package management tool, I highly recommend using nvm for setting it up.

The project structure includes:

├── lib # our compiled cljs js file
├── Makefile # nodejs build tasks
├── node_modules # npm local libraries
├── package.json # npm dependencies
├── project.clj # lein cljs build and dependencies
├── src # cljs source
├── test # compiled test js file
└── test-cljs # cljs test code

The project.clj contains our cljs build settings and dependencies:

(defproject celestial-node "0.1.0-SNAPSHOT"
  :description "Celestial nodejs integration"
  :url ""
  :license {:name "Apache V2" :url ""}
  :dependencies [[org.clojure/core.incubator "0.1.2"]
                 [org.bodil/redlobster "0.2.1"]
                 [litmus "0.2.0-SNAPSHOT"]]
  :plugins  [[lein-cljsbuild "0.3.0"]]
  :cljsbuild {
               {:source-paths ["src"]
                :compiler {
                           :target :nodejs
                           :output-to "lib/celestial.js"
                           :optimizations :simple
                           :pretty-print true}}
               {:source-paths ["test-cljs"]
                :compiler {
                           :target :nodejs
                           :output-to "test/celestial.js"
                           :optimizations :simple
                           :pretty-print true}}}}

Notice that there are two builds with two different outputs, one for production use (lib/celestial.js) and one for testing (test/celestial.js), this enable us to keep test logic out of our production code (in fact the test run executes as a part of the main) , in order to build the cljs output we could run:

 # one time compilation
 $ lein cljsbuild once 
 # auto compilation on save
 $ lein cljsbuild auto


Another key aspect is a testing framework, most cljs testing frameworks deal with testing browser code (and require phantom js), the only one that iv found to run well on nodejs and has a cljs DSL is litmus which wrapps around mocha.js , currently its not up on Clojars so build it locally using lein install.

The following show cases how a litmus test looks like:

 (describe "system manipulations"
   (given "we store a new system"  
      (it-async "creates a new id"    
        (create-system (slurp-edn "fixtures/redis-system.edn") 
            (fn [body] (reset! sys-id (aget body "id")) (done))
            (fn [error] (println "failed" error) (done))))
      (it-async "we can fetch it back"
        (get-system @sys-id 
            (fn [body] (equals? (aget body "type") => "redis") (done))
            (fn [error] (println error))))    

Due to the async nature of nodejs we use done fn to mark when a test is indeed done, the DSL is BDD oriented, in order to run the tests we run the 'make test' defined in our Makefile (which is a part of the nodejs build system), the Makefile consists of:

        @NODE_ENV=test ./node_modules/.bin/mocha \
        --reporter $(REPORTER) \
        --ui tdd -t 3000
        @NODE_ENV=test ./node_modules/.bin/mocha \
        --reporter $(REPORTER) \
        --growl \
        --ui tdd \

package: clean
        lein cljsbuild once
        mkdir pkg
        cp lib/celestial.js pkg
        cp -r fixtures pkg
      rm -rf pkg

.PHONY: test test-w

As you can see the test target invokes the mocha binary located under npm's node_modules library which is defined in the package.json file:

  "name": "celestial-node",
  "preferGlobal": false,
  "version": "0.1.0",
  "author": "Ronen Narkis <> (",
  "description": "Celestial API for nodejs",
  "repository": {
    "type": "git",
    "url": ""
  "license": "Apache-V2",
  "dependencies": {
    "npm": ">= 1.1.2",
    "request": "=2.21.0"
  "scripts": {
    "test": "make test"
  "devDependencies": {
    "chai": "*",
    "mocha": "*"
  "optionalDependencies": {},
  "engines": {
    "node": "0.6 || 0.7 || 0.8"
  "homepage": "",
  "main": "lib/celestial.js"

Nodejs integration:

The package.json includes all our nodejs dependencies (remeber the duality part?), we can add and use any nodejs module from our cljs code, in order to use a nodejs module:

; nodejs require
(def request (js/require "request")) 

; js interop usage
(defn GET [url s f]
  (.get request (<< "~(@conf :url)~{url}") (clj->js (opts)) (response- s f)))

In order to expose cljs api to nodejs consumers we need to export a ns:

(ns celestial.core ...)
(defn main [])

; required even if we don't use a main
(set! *main-cli-fn* main)

; export this ns as a part of nodejs module
(aset js/exports "core" celestial.core)

With that all in place we can require our cljs module from any other npm enabled project:

  "name": "hubot-celestial",
  "version": "0.0.1",
  "description": "Hubot script for interacting with Celestial",
  "main": "main.js",
  "scripts": {
  "repository": "git://",
  "author": "",
  "license": "Apache-V2",
  "dependencies": {
    "coffee-script": "~1.4.0",
    "hubot": "~2.4.8",
    "hubocator": "0.1.2",
    "cli-table" : "0.2.0",
    "underscore" :"1.4.4",

Requiring the api:

celestial = require ('celestial-node')
celestial.core.get_system(id,((b)-> msg.send systemTable(b)), ((e)-> msg.send e))


Iv found cljs and nodejs to be a very powerfull (yet a bit young) combo to work with, it offers yet another very rich platform to run Clojure code on top of. I hope you will find it useful too.


Tags: js Clojure nodejs