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Reduce boilerplateλ︎

The previous section explained some important fundamental concepts around the Google Closure Library. However it also involved a substantial amount of boilerplate. We can eliminate this boilerplate by specifying a :main entry point in the options that we pass to cljs.build.api/build. Let's do that now:

(require 'cljs.build.api)

(cljs.build.api/build "src"
  {:main 'hello-world.core
   :output-to "out/main.js"})

Change your HTML to the following:

<html>
    <body>
        <script type="text/javascript" src="out/main.js"></script>
    </body>
</html>

Rebuild on Mac or GNU/Linux:

java -cp cljs.jar:src clojure.main build.clj

On Windows: 

java -cp "cljs.jar;src" clojure.main build.clj

Refresh the page and you should still see "Hello world!" printed to the JavaScript console. If you examine out/main.js you'll see that it writes out the boilerplate script tags for you. The previous contents of main.js are now in out/cljs_deps.js, which is loaded alongside our namespace by the new out/main.js.