GWT compiles Java to JavaScript, right? So compile the Swing calls into calls to equivalent JavaScript UI library calls. Barf if they try to do stuff you can't

GWT compiles Java to JavaScript, right? So compile the Swing calls into calls to equivalent JavaScript UI library calls. Barf if they try to do stuff you can't do in JavaScript (filesystem), as GWT surely has to do already. (disclaimer: never coded GWT in my life)