cljs.js/require

(defn require
  ([name cb]
    (require name nil cb))
  ([name opts cb]
    (require nil name opts cb))
  ([bound-vars name opts cb]
   (require bound-vars name nil opts cb))
  ([bound-vars name reload opts cb]
   (let [bound-vars (merge
                      {:*compiler*     (env/default-compiler-env)
                       :*data-readers* tags/*cljs-data-readers*
                       :*load-macros*  (:load-macros opts true)
                       :*analyze-deps* (:analyze-deps opts true)
                       :*load-fn*      (or (:load opts) *load-fn*)
                       :*eval-fn*      (or (:eval opts) *eval-fn*)}
                      bound-vars)
         aname (cond-> name (:macros-ns opts) ana/macro-ns-name)]
     (when (= :reload reload)
       (swap! *loaded* disj aname))
     (when (= :reload-all reload)
       (reset! *loaded* #{}))
     (when (:verbose opts)
       (debug-prn (str "Loading " name (when (:macros-ns opts) " macros") " namespace")))
     (if-not (contains? @*loaded* aname)
       (let [env (:*env* bound-vars)]
         (try
           ((:*load-fn* bound-vars)
             {:name name
              :macros (:macros-ns opts)
              :path (ns->relpath name)}
             (fn [resource]
               (assert (or (map? resource) (nil? resource))
                 "*load-fn* may only return a map or nil")
               (if resource
                 (let [{:keys [lang source cache source-map file]} resource]
                   (condp keyword-identical? lang
                     :clj (do
                            (pre-file-side-effects (:*compiler* bound-vars) aname file opts)
                            (eval-str* bound-vars source name (assoc opts :cljs-file file)
                              (fn [res]
                                (post-file-side-effects file opts)
                                (if (:error res)
                                  (cb res)
                                  (do
                                    (swap! *loaded* conj aname)
                                    (cb {:value true}))))))
                     :js (process-macros-deps bound-vars cache opts
                           (fn [res]
                             (if (:error res)
                               (cb res)
                               (process-libs-deps bound-vars cache opts
                                 (fn [res]
                                   (if (:error res)
                                     (cb res)
                                     (let [res (try
                                                 ((:*eval-fn* bound-vars) resource)
                                                 (when cache
                                                   (load-analysis-cache!
                                                     (:*compiler* bound-vars) aname cache)
                                                   (ana/register-specs cache))
                                                 (when source-map
                                                   (load-source-map!
                                                     (:*compiler* bound-vars) aname source-map))
                                                 (catch :default cause
                                                   (wrap-error
                                                     (ana/error env
                                                       (str "Could not require " name) cause))))]
                                       (if (:error res)
                                         (cb res)
                                         (do
                                           (swap! *loaded* conj aname)
                                           (cb {:value true}))))))))))
                     (cb (wrap-error
                           (ana/error env
                             (str "Invalid :lang specified " lang ", only :clj or :js allowed"))))))
                 (cb (wrap-error
                       (ana/error env
                         (ana/error-message (if (:macros-ns opts)
                                              :undeclared-macros-ns
                                              :undeclared-ns)
                           {:ns-sym name :js-provide (cljs.core/name name)})))))))
           (catch :default cause
             (cb (wrap-error
                   (ana/error env
                     (str "Could not require " name) cause))))))
       (cb {:value true})))))