You don't need to use new js.JsFunction.withThis
. In your case just use :
js.context['myHyperSuperMegaFunction'] = myHyperSuperMegaFunction;
For your information new js.JsFunction.withThis
has to be used when you need to use the this
Js context. In your error, you can see that the first parameter is Instance of 'Window'
which is the global context in Js.