In GraphDB, if I register a javascript function f in GraphDB with

prefix extfn:<http://www.ontotext.com/js#>
INSERT DATA {
    [] <http://www.ontotext.com/js#register> '''
        function f(x) { ... }
      '''

What will be the class of x if f is called with an IRI or blank node as argument, i.e. not a String? The method invokation x.constructor yields undefinedso it's difficult to figure out what's its type.