Support specifying requirejs modules for comm targets

IPython/html/static/services/kernels/comm.js

@@ -65,20 +65,40 @@ define([
     
     CommManager.prototype.comm_open = function (msg) {
         var content = msg.content;
-        var f = this.targets[content.target_name];
-        if (f === undefined) {
-            console.log("No such target registered: ", content.target_name);
-            console.log("Available targets are: ", this.targets);
-            return;
-        }
-        var comm = new Comm(content.target_name, content.comm_id);
-        this.register_comm(comm);
-        try {
-            f(comm, msg);
-        } catch (e) {
-            console.log("Exception opening new comm:", e, e.stack, msg);
-            comm.close();
-            this.unregister_comm(comm);
+        var that = this;
+        
+        var instantiate_comm = function(target) {
+            var comm = new Comm(content.target_name, content.comm_id);
+            that.register_comm(comm);
+            try {
+                target(comm, msg);
+            } catch (e) {
+                console.log("Exception opening new comm:", e, e.stack, msg);
+                comm.close();
+                that.unregister_comm(comm);
+            }
+        };
+
+        if (content.target_module) {
+            // Load requirejs module for comm target
+            require([content.target_module], function(mod) {
+                var target = mod[content.target_name];
+                if (target !== undefined) {
+                    instantiate_comm(target)
+                } else {
+                    console.log("Comm target " + content.target_name + 
+                        " not found in module " + content.target_module);
+                }
+            }, function(err) { console.log(err); });
+        } else {
+            // No requirejs module specified: look for target in registry
+            var f = this.targets[content.target_name];
+            if (f === undefined) {
+                console.log("No such target registered: ", content.target_name);
+                console.log("Available targets are: ", this.targets);
+                return;
+            }
+            instantiate_comm(f)
         }
     };