Recently a colleague wanted to use an OOB UI page but wanted to amend its behaviour. We could see that a jvar_variable available that if set, would do exactly what we wanted. However, we didn’t want to edit the UI page to do manually set it. Well it turns out setting the variable was far easier than writing a single piece of jelly.
Passing data into a UI page usually consists of adding “sysparm_something” as a URL paremeter when calling the UI page. Well it turns out, you can actually pass anything in. So my colleague showed me that by passing the jvar_variable as a URL parameter, it was actually be set correctly.