When I was using IE11's dev tools (i.e. F12 key), I could not find "unhandled exceptions". Nonetheless, I went to the editor, and then I opened up the dev tools. I found this error:
SCRIPT16389: Unspecified error.
File: index.php, Line: 1, Column: 1
This occurs only when I don't open the dev tools until after I open the editor.
Moreover, when I used the scroll menu from the Edittools and then changed from one submenu to another (e.g. "Templates" to "Wikicode", I found this warning (not an error):
DOM7011: The code on this page disabled back and forward caching. For more information, see: http://go.microsoft.com/fwlink/?LinkID=291337
File: index.php
Then I chose to pause on "all exceptions"; I found multiple warnings saying that specific syntax codes (or tools?) are "deprecated".
Then I went to Chrome's dev tools. I found one "warning" message:
Use of "skin" is deprecated. Use mw.config instead.
It also came with the link: https://en.wikinews.org/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki%7Cmediawiki.legacy.wikibits&only=scripts&skin=vector&version=0upuj5q
Also, when I clicked on the scroll menu, one of "verbose" messages appears:
[Violation] Added non-passive event listener to a scroll-blocking 'mousewheel' event. Consider marking event handler as 'passive' to make the page more responsive. See https://www.chromestatus.com/feature/5745543795965952
This link came with it: https://en.wikinews.org/w/index.php?title=Wikinews:Water_cooler/policy&action=edit§ion=new#
Then I went to Firefox's. I found this warning:
Use of "skin" is deprecated. Use mw.config instead.
Other browsers' dev tools have this similar message. I could not find exceptions or errors, according to Firefox's dev tools. I found another message:
JQMIGRATE: Migrate is installed with logging active, version 3.0.1
Other browsers' dev tools receive the same message, but they don't treat it like a warning (or something like that).