A key utility for helping Visual Builder developer debug and resolve issues in their application is the output generated into the browser console by the VB runtime libraries. I've wrote about how to control the logging level produced in a past blog entry. If however you are working on developing App UI extensions for Oracle Fusion Cloud Apps you might have noticed that the default logging level you get is only showing errors. It's quite easy to get more granular logging information if you need it.
Using your browser's develper tools section, go into the Application->Local Storage section and locate the VB Studio instance you are using.
Scroll the list of variables until the end and click the empty space to create a new variable. The key is:
vb_logConfig_level
For the value you can use one of the following: error, warning, info, fine, and finer.
Now if you'll refresh your page you'll start to see much more information about the things your App UI extension is doing.