cljs.js/append-source-map

(defn append-source-map
  [state name source sb sm-data {:keys [output-dir asset-path] :as opts}]
   (let [t    (.valueOf (js/Date.))
         smn  (if name
                (string/replace (munge (str name)) "." "/")
                (str "cljs-" t))
         ts   (.valueOf (js/Date.))
         out  (or output-dir asset-path)
         src  (cond-> (str smn ".cljs?rel=" ts)
                out (prefix (str out "/")))
         file (cond-> (str smn ".js?rel=" ts)
                out (prefix (str out "/")))
         json (sm/encode {src (:source-map sm-data)}
                {:lines (+ (:gen-line sm-data) 3)
                 :file  file :sources-content [source]})]
     (when (:verbose opts) (debug-prn json))
     (swap! state assoc-in
       [:source-maps name] (sm/invert-reverse-map (:source-map sm-data)))
     (.append sb
       (str "\n//# sourceURL=" file
            "\n//# sourceMappingURL=data:application/json;base64,"
            (base64/encodeString json)))))