This is probably just wishful thinking...
Is there any way to check to see if an ASP/VBScript function is defined before calling it?
Here is my solution which works on the same principle, but the hacky-ness is pretty self-contained:
Function FunctionExists( func_name )
FunctionExists = False
On Error Resume Next
Dim f : Set f = GetRef(func_name)
If Err.number = 0 Then
FunctionExists = True
End If
On Error GoTo 0
End Function