"Guided Application Creator is enabled via the Guided Application Creator (com.glide.sn-guided-app-creator) plugin, which is active by default in the Now Platform." Located under "Activation Information" section at this URL:
https://docs.servicenow.com/en-US/bundle/tokyo-application-development/page/build/guided-app-creator
/concept/guided-app-creator.html

https://developer.servicenow.com/dev.do#!/learn/learning-plans/rome/new_to_servicenow
/app_store_learnv2_scripting_rome_debugging_client_scripts
The following are debugging strategies for client-side scripts, which run in the web browser and manipulate the user interface:
* g_form.addInfoMessage(). This is a client-side API that displays an information message at the top of the form.
* Field Watcher. This is a debugging tool that displays the current and previous values of one or more fields on a form.
* jslog(). This is a client-side API that writes a message to the browser console.
The following is not a debugging strategy for client-side scripts, but for server-side scripts, which run on the ServiceNow platform and manipulate the database:
* gs.log(). This is a server-side API that writes a message to the system log. References: Client-Side Scripting APIs, Debugging Client Scripts