Add the simple endpoint and the configuration.

src/main/blog/core.cljs

@@ -0,0 +1,15 @@
+(ns blog.core
+  (:require ["express" :as express]))
+
+(def app (express))
+(def port 3000)
+
+(defn main []
+  (. app get "/"
+     (fn [req res]
+       (. res send "Hello world")))
+
+  (. app listen port
+     (fn []
+       (println "Listen on " port))))
+