Already during implementing itcl in javascript there was the decision to use wtk as the frontend for GUI building. It is based on the idea to separate the data and administration part of the GUI from the presentation part. The communication between the two parts can be done in different ways: Using a direct function call to the wtk functions Using a client/server solution which is running the client part (mostly the presentation part in javascript) in the browser and the server part (mostly the Tcl part) on the serving machine