Google Maps with Clojurescript.
Clojure JavaScript
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What is Contour?

Contour is Google Maps v3 web app written entirely in ClojureScript! In other words, it's awesome.

Very early days. We have a demo on Heroku.


The project rides on Compojure, a framework for writing web applications in Clojure.

It also rides on ClojureScript which is a compiler for Clojure that emits JavaScript code! For bonus points it's also compatible with the with the advanced compilation mode of Google Closure optimizing compiler.

But wait, there's more! As an extra bonus, Contour additionally rides on lein-cljsbuild, a leiningen plugin that makes it easy (and quick) to compile ClojureScript source into JavaScript. It's similar to cljs-watch but uses lein instead of a standalone executable.

Show me CODE

Here's a side-by-side of JavaScript and ClojureScript. The "Hello World" of Google Maps in JavaScript looks like this:

    var map;

    function initialize() {
        var myOptions = {
            zoom: 8,
            center: new google.maps.LatLng(-34.397, 150.644),
            mapTypeId: google.maps.MapTypeId.ROADMAP
        map = new google.maps.Map(document.getElementById('map_canvas'), myOptions);

    google.maps.event.addDomListener(window, 'load', initialize);

The "Hello World" of Google Maps in ClojureScript looks like this:

    (def *map* nil)

    (def my-opts
      {"zoom" 8
       "mapTypeId" google.maps.MapTypeId.ROADMAP
       "center" (google.maps.LatLng. -34.397, 150.644)})

    (defn map-load []
      (let [elem (goog.dom/getElement "map_canvas")]
        (set! *map* (google.maps.Map. elem my-opts))))

    (events/listen js/window "load"

Let's get started

To get started, you'll need to clone Contour and install Leinigen, the build tool for Clojure.

Clone Contour

Fire up your command line and:

$ git clone
$ cd contour

Install Leiningen

Next install Leiningen:

  • Download this script which is named lein
  • Place it on your path so that you can execute it. (I like to use ~/bin)
  • Set it to be executable. (chmod 755 ~/bin/lein)

Set this environment variable:

export RING_ENV='development'


$ cd contour

# Download the dependencies:
$ lein deps

# Open a new terminal window and:
$ lein cljsbuild auto

# Open a new terminal window and:
$ lein ring server

That should open a browser window at You're all set!


Copyright © 2013 Sam Ritchie

Distributed under the Eclipse Public License, the same as Clojure.