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Adding ClojureScript to Chat Room Demo

In the last iteration of our demo we add ClojureScript to improve our simple chat server from Demo 3. We will poll server using XhrIo request to fetch new chat room messages without page refresh.


We use lein-cljsbuild Leiningen plugin to integrate ClojureScript to our project. See project.clj for changes and cljsbuild configuration.

Type lein cljsbuild once to compile .cljs files to JavaScript.

To modify our ClojureScript life in the browser, we can also start ClojureScript REPL using lein cljsbuild repl-listen. This command will listen for repl request on port 9000. Then we need to connect the browser.

Once we compile ClojureScript files, we can launch Jetty web server, point our browser to main page and enter a chat room. Then we launch JavaScript developer console in Chrome and type demo.repl.start_repl ().


Crossovers in Cljsbuild enable code sharing between Clojure and ClojureScript. ClojureScript files are stored in src-cljs/ directory, crossovers are in stored in src/ directory and configured in project.clj file.

We will use crossover functionality to share message rendering in message.clj. Output from function render-message can be rendered into HTML by both Hiccup library and clojure.browser.dom.

Extending server

To enable ClojureScript polling we performed two changes to core.clj:

  • (resources "/") to serve compiled JavaScript files from resources/ directory.
  • we added api-routing to fulfill browser polling requests.

In page.clj we included JavaScript and added new attributes to identify messages from JavaScript.

Server polling from browser

ClojureScript uses Google Closure library. We use and goog.Timer to build simple polling mechanism.

clojure.browser.dom, net and event libraries are simple ClojureScript wrappers around Google Closure functionality.