Load extensions on client-side only if its extension.js file exists.

vispa/static/js/extensions.js

@@ -40,16 +40,21 @@ define(["jquery", "emitter", "vispa/module", "vispa/ui"], function($, Emitter, M
     loadExtension: function(name) {
       var self = this;
       this.extensionsLoading++;
-      require(["extensions/"+name+"/static/js/extension"],
-        this.registerExtension.bind(this),
-        function(err) {
+
+      // check if the entry point, i.e. the extension.js file, exists
+      var entryPoint = "extensions/" + name + "/static/js/extension";
+
+      $.ajax({ url: entryPoint + ".js", type: "HEAD" }).fail(function() {
+        self._checkExtensionsLoaded();
+      }).done(function() {
+        require([entryPoint], self.registerExtension.bind(self), function(err) {
           if (vispa.args.global.devMode) {
             self.logger.error("extension '%s' failed to load due to: %s",
               err.requireModules[0].split("/")[1], err.requireType);
           }
           self._checkExtensionsLoaded();
+        });
       });
-      
     },
     
     start: function start() {