Skip to content
Clojure to JS compiler (patched to allow compiling of compiler to ClojureScript)
Branch: cljs_in_cljs
Clone or download
Pull request Compare This branch is 144 commits ahead, 4136 commits behind clojure:master.
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.

ClojureScript Compiler Compiled with ClojureScript?

This is a patched version of the ClojureScript compiler that compiles to ClojureScript. Normally, the ClojureScript compiler is a pure Clojure program that runs on the JVM. This patched version runs from the compiled JavaScript. This project was kicked off by kanaka and chouser during some intense hacking at Clojure/conj 2012. Kanaka continues to develop the fork towards the goal of being fully self-hosting (i.e. ClojureScript-in-ClojureScript).


  • Why not?
  • Compilers are only cool once they are self-hosting (can compile their own code). This fork is not self-hosting yet, but that is the goal.
  • You can use ClojureScript without a JVM.
  • You can have a ClojureScript REPL web app that runs locally in your browser (no server involved after loading the page).

Current Caveats

  • JavaScript output is not optimized by the Google Closure Compiler (which is a Java program).
  • The code changes are not all compatible with the normal Clojure ClojureScript (JVM based) compiler. To make it compatible we really need Feature Expressions in Clojure
  • The :nodejs compilation target is currently broken. However, the node/run.js bootstrap script enables compiled CLJS code to be invoked that was not compiled with a :target.
  • Other miscellaneous broken things that have not been tracked down yet.


  • numeric keywords (:2) are broken
  • anonymous functions do not warn about arity
  • Unicode symbol breakage
  • hex numbers "0x7e7"
  • warnings during compile about unchecked-if


  • update to upstream ClojureScript
  • file I/O (at least on the node.js side)
  • misc functionality: require, use, var metadata, :private def check
  • self-hosting (compile ClojureScript compiler using node.js hosted ClojureScript compiler)
  • optional optimizations (single JS file output, etc)
  • tagged reader literals
  • get test/cljs/cljs/core_test.cljs to load/run successfully
  • line numbered errors
  • single file output and performance optimizations (without unused code removal)
  • better long line/multiline editing in web REPL


The ClojureScript-in-ClojureScript compiler is compiled using Clojure (i.e. on the JVM).

First, run ./script/bootstrap which downloads the necessary dependencies: Clojure, Google Closure Library, Google Closure Compiler, and Rhino. This must be run from the root project directory.

Next, run ./script/compile to build the compiler. This might give off some warnings, but that's okay.

You should now have a functioning ClojureScript compiler at ./bin/cljs.


The ./bin/cljsc script takes a file or project directory containing .cljs files. It creates an out folder with your compiled JavaScript. It optionally accepts a second argument with Google Closure Compiler options, although it currently won't work with any optimization mode other than {:optimizations :none} (the default).

After building a cljs project, you will need to copy ./src/cljs/goog.js into the out directory created by compilation if it doesn't already exist there.



There is a sample project (a web-based REPL) you can build and play with inside the web directory.

It comes with a build script:

cd web

Now open the web/repl.html file in a browser.

Node.js REPL

For a REPL in Node.js, build the src/cljs/noderepl.cljs code:

cd node
../bin/cljsc ../noderepl.cljs > noderepl.js
cp ../src/cljs/goog.js out/

Now use the run.js bootstrap code to launch the repl:

./run.js noderepl.js

Node.js compilation/evaluation

For direct *.cljs file compilation/evaluation, build the nodecljs.cljs compiler:

cd node
../bin/cljsc ../src/cljs/nodecljs.cljs > nodecljs.js
cp ../src/cljs/goog.js out/

You can now use a combination of the run.js bootstrap code and nodecljs.js to compile/evaluate the hello.cljs file:

./run.js nodecljs.js hello.cljs

What is ClojureScript?

ClojureScript is a new compiler for Clojure that targets JavaScript. It is designed to emit JavaScript code which is compatible with the advanced compilation mode of the Google Closure optimizing compiler.

Getting Started

Questions, Feedback?

Please point all of your questions and feedback here.

Developers Welcome

ClojureScript operates under the same license as Clojure. All contributors must have a signed CA (Contributor's Agreement) and submit their patch via the appropriate channels. If you're interested in contributing to the project, please see the contributing page on


Copyright (c) Rich Hickey. 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.
You can’t perform that action at this time.