how do I run a trusted function?

If I define a trusted function in a folder level JS script, how do I actually call this from my javascript on a form? e.g. if my trusted function is:
var myFileOpen = app.trustedFunction(
function() {

app.beginPriv();
app.browseForDoc();
app.endPriv();
}
});

How do I access the function from say a button on an XFA form?

Thanks.