Reagent - ClojureScript and React made easy


Recently I’ve started reading into Clojure and came across something really interesting.

Clojure is a JVM based functional programming language, based on Lisp. React is a recent web frontend framework from Facebook that has been everywhere lately. React a reactive Javascript framework, similar to AngularJS, but takes a different approach in component management to make it much faster and more scalable.

Now this is where it gets interesting - Clojure can be compiled to Javascript via the ClojureScript plugin. Combine the two and you get Reagent, a framework that integrated them together nicely.

Starting a Reagent Project - in 3 steps

There are two ways to run ClojureScript + React, the first to build multi page app and build both server and client side in Clojure, the other way is to just build the frontend with it as a single page app. We’re much more interested in the latter.

  • First download and install Leiningen for building Clojure. Once installed, we can generate the project a new Reagent frontend project with this easily by running:
  lein new reagent-frontend myproject
  • To run it:
cd myproject
lein cljsbuild auto
  • Open the html file with your browser

You should see the ‘Welcome to Reagent’ demo page. Simple!

How did it work?

The Clojure script in


got compiled into a Javascript file at


The index.html page does nothing more than including that Javascript file, and voila!

Making things happen reactively

Now let’s have a look at the reactive part by demoing the obligatory live counter button. Update your core.cljs file to the following:

(ns myproject.core
    (:require [reagent.core :as r :refer [atom]]
              [reagent.session :as session]
              [secretary.core :as secretary :include-macros true]))

;; -------------------------
;; Views

(defonce click-count (r/atom 0))

(defn home-page []
    [:h2 "Welcome to Reagent"]
    [:p "Just playin around..."]
    [:input {:type "button" :value "click this" :on-click #(swap! click-count inc)}]
    [:p "i've been clicked for: " @click-count]

;; -------------------------
;; Initialize app

(defn mount-root []
  (r/render [home-page] (.getElementById js/document "app")))

(defn init! []

Refresh the index.html page and you will see the button, with a counter below that increments count on click.

Notice the component is ‘mounted’ to a HTML tag, and the content of the tag are eventually rendered via Javascript, this is React’s framework in action. ClojureScript works nicely here with it’s tag almost always matching the HTML ones, while not being as clutered as HTML itself - it reminds me of the lovely Jade template in NodeJS.

Demo code available on Github

More Reading

That’s all for now, I got to go hone up my Clojure skills!

Post Directory