This is a leiningen plugin that makes it easy (and quick) to compile ClojureScript source into JavaScript. It's similar to [cljs-watch] 1, but is driven via lein instead of via a standalone executable. This means that your project can depend on a specific version of lein-cljsbuild, fetch it via lein deps, and you don't have to install any special executables into your PATH.

Also, this plugin has built-in support for seamlessly sharing code between your Clojure server-side project and your ClojureScript client-side project.

You can install the plugin via lein:

$ lein plugin install emezeske/lein-cljsbuild 0.0.5

Or by adding lein-cljs to your project.clj file in the :dev-dependencies section:

(defproject lein-cljsbuild-example "1.2.3"
  :dev-dependencies [[emezeske/lein-cljsbuild "0.0.5"]])

Make sure you pull down the jar file:

$ lein deps

See the example-projects directory for a couple of simple examples of how to use lein-cljsbuild.

The lein-cljsbuild configuration is specified under the :cljsbuild section of your project.clj file. A simple project might look like this:

(defproject lein-cljsbuild-example "1.2.3"
  :dev-dependencies [[emezeske/lein-cljsbuild "0.0.5"]]
  :cljsbuild {
    ; The path to the top-level ClojureScript source directory:
    :source-path "src-cljs"
    ; The standard ClojureScript compiler options:
    ; (See the ClojureScript compiler documentation for details.)
    :compiler {
      :output-to "war/javascripts/main.js"  ; default: main.js in current directory
      :optimizations :whitespace
      :pretty-print true}})

If you'd like your ClojureScript to be compiled whenever you run lein compile, you can also add the following entry to your defproject config:

:hooks [leiningen.cljsbuild]

Once the plugin is installed, you can build the ClojureScript once:

$ lein cljsbuild once

Or you can have lein-cljsbuild watch your source files for changes and automatically rebuild them. This is recommended for development, as it avoids the time-consuming JVM startup for each build:

$ lein cljsbuild auto

Sharing code with lein-cljsbuild is accomplished via the configuration of "crossovers". A crossover specifies a namespace in your Clojure project, the content of which should be copied into your ClojureScript project. The files in the Clojure directory will be monitored and copied over when they are modified. Of course, remember that since the namespace will be used by both Clojure and ClojureScript, it will need to only use the subset of features provided by both languages.

Assuming that your top-level directory structure looks something like this:

├── src-clj
│   └── example
│       ├── core.clj
│       ├── something.clj
│       └── crossover
│           ├── some_stuff.clj
│           └── some_other_stuff.clj
└── src-cljs
    └── example
        ├── core.cljs
        ├── whatever.cljs
        └── util.cljs

And your project.clj file looks like this:

(defproject lein-cljsbuild-example "1.2.3"
  :dev-dependencies [[emezeske/lein-cljsbuild "0.0.5"]]
  :source-path "src-clj"
  :cljsbuild {
    :source-path "src-cljs"
    ; Each entry in the :crossovers vector describes a Clojure namespace
    ; that is meant to be used with the ClojureScript code as well.
    ; The files that make up this namespace will be automatically copied
    ; into the ClojureScript source path whenever they are modified.
    :crossovers [example.crossover]
    :compiler {
      :output-to "war/javascripts/main.js"  ; default: main.js in current directory
      :optimizations :whitespace
      :pretty-print true}})

Then lein-cljsbuild would copy files from src-clj/example/crossover to src-cljs/example/crossover, and you'd end up with this:

├── src-clj
│   └── example
│       ├── a_file.clj
│       ├── core.clj
│       └── crossover
│           ├── some_stuff.clj
│           └── some_other_stuff.clj
└── src-cljs
    └── example
        ├── a_different_file.cljs
        ├── crossover
        │   ├── some_stuff.cljs
        │   └── some_other_stuff.cljs
        ├── whatever.cljs
        └── util.cljs

With this setup, you would probably want to add src-cljs/example/crossover to your .gitignore file (or equivalent), as its contents are updated automatically by lein-cljsbuild.

In ClojureScript, macros are still written in Clojure, and can not be written in the same file as actual ClojureScript code. Also, to use them in a ClojureScript namespace, they must be required via :require-macros rather than the usual :require.

This makes using the crossover feature to share macros between Clojure and ClojureScript a bit difficult, but lein-cljsbuild has some special constructs to make it possible.

Three things need to be done to use lein-cljsbuild to share macros.

These examples assume that your project uses the src-clj/example/crossover directory, and that all of the macros are in a file called src-clj/example/crossover/macros.clj.

Add this magical comment to any crossover files that contain macros:

;*CLJSBUILD-MACRO-FILE*;

This tells lein-cljsbuild to keep the .clj file extension when copying the files into the ClojureScript directory, instead of changing it to .cljs as usual.

In any crossover Clojure file, lein-cljsbuild will automatically erase the following string (if it appears):

;*CLJSBUILD-REMOVE*;

This magic can be used to generate a ns statement that will work in both Clojure and ClojureScript:

(ns example.crossover.some_stuff
  (:require;*CLJSBUILD-REMOVE*;-macros
    [example.crossover.macros :as macros]))

Thus, after removing comments, Clojure will see:

(ns example.crossover.some_stuff
  (:require
    [example.crossover.macros :as macros]))

However, lein-cljsbuild will remove the ;*CLJSBUILD-REMOVE*; string entirely, before copying the file. Thus, ClojureScript will see:

(ns example.crossover.some_stuff
  (:require-macros
    [example.crossover.macros :as macros]))

And thus the macros can be shared.

Source Copyright © Evan Mezeske, 2011-2012. Released under the Eclipse Public License - v 1.0. See the file COPYING.

• Evan Mezeske (Author) ([email protected])
• Shantanu Kumar ([email protected])