Issue
Symptoms
GlideAjax is supported in Client Scripts in Service Portal, but it is not currently supported in the Client Controller of a Widget. Script Include functions are only accessible in the Server Script of the widget.
Additional Information
The Community post below describes how to create a Script Include that can be used in any widget's server script for specific applications.
https://community.servicenow.com/community?id=community_question&sys_id=28e38fa5dbd8dbc01dcaf3231f9619b4
The class object can be directly initialized without using GlideAjax. Client script calling Server Script method is possible using c.server.get.