found the problem.

whalesong/js-assembler/package.rkt

@@ -292,10 +292,13 @@ M.modules[~s] =
 (define (assemble-modinvoke path after)
   (let ([name (rewrite-path (path->string path))]
         [afterName (gensym 'afterName)])
-    (format "var ~a = function() { ~a };
+    (format "
+        var ~a = function() { ~a };
+        plt.runtime.PAUSE(function(restart) {
              plt.runtime.currentModuleLoader(M,
                                              ~s,
                                              function() {
+                                                restart(function(M) {
                                                     if (! M.modules[~s].isInvoked) {
                                                         M.modules[~s].internalInvoke(M,
                                                                                      ~a,
@@ -303,11 +306,12 @@ M.modules[~s] =
                                                     } else {
                                                         ~a();
                                                     }
+                                                })
                                              },
                                              function() {
                                                 alert('Could not load ~s');
                                              })
-             "
+       });     "
             afterName
             after
             (symbol->string name)