Simple POST function in ClojureScript and Node.js
Looks great! Some minor suggestions; pull the parsed-url aset into a doto, and that naming the request req isn't very useful. Prefer dash to underscore.

(let [parsed-url (doto (.parse url url_str)
                   (aset "method" "POST"))]
  (doto (.request http parsed-url cb)
    (.write data)
    (.end)))