I keep forgetting about that. Wish it was in the documentation.
When testing this I wondered how using this method you could pass a variable on.
And realised you could change one of the standard hypeDocument, element, event ones to an array.
So in the first js code you would have something like:
hypeDocument.functions().js2(hypeDocument, [element,"hello"], event);
And in the js2() functions code you would have someone like:
var element_ = element;
var fooString = element;