Convenience function to retrieve any params that were part of the requested page. The param values returned come from "httr::parse_url()"
get_query_param(field = NULL, session = shiny::getDefaultReactiveDomain())The full list of params on the URL (if any), as a list. Or, the single requested param (if present). Or NULL if there's no input, or no params.
If provided, retrieve only a param with this name. (Otherwise, return all params)
The Shiny session