[Ur] Calling an Ur/Web function from Javascript

[Istvan Chung]

I'm trying to use the FFI to call an Ur/Web function from javascript,
but there's very little in the manual about this; how can I do this? At
present, anything I've tried has failed at compile time with the error:
"Unsupported FFI function Module.functionName in JavaScript"

Also, although there's an explanation of how Ur/Web objects are
marshalled to javascript types, what of the reverse: how are javascript
objects marshalled to Ur/Web types?

Thanks
-- 
Istvan Chung