You cannot create new functions on Glide objects such as GlideUser.
What are you trying to do?
If you need data on the client side and it is static for the life of the form, look at business rules that run at Display time and populate g_scratchpad.
If you need to make arbitrary server-side queries and calculations, use GlideAjax.
If you want to filter references and choices that depend on earlier selections, there are ways to avoid writing Ajax queries by issuing javascript: calls from the reference qualifier and using attributes to specify which values are dynamic.
