Several of admin_toolbars JS files/behaviors depend on core libraries (e.g. core/drupal, core/jquery, core/once) but do not explicitly declare those dependencies in admin_toolbar.libraries.yml.
This hasn't proven an issue in the past, as they all declare a dependency on admin_toolbar/toolbar.tree, which, in turn depends on toolbar/toolbar (core's Toolbar module), which has ensured that all the necessary libraries were available.
An evaluation of core's approach to dependencies indicates this may not be best practice (what happens if the lib you were depending one to load all those dependencies drops one or more of them?). That suggests that admin_toolbar should explicitly declare any dependencies for each file/behavior.
Decide on whether or not to declare all dependencies, evaluate each JS file and make the appropriate changes to admin_toolbar.libraries.yml.
-OR-
Stick with the current approach and close this issue.
None
None
None
Active
3.6
Code
Explicitly adding dependencies makes it less likely the module will break in the future, at the cost of having to explicitly declare them once. Unless a dependency name changes while it's functions don't or something kind of bizarre like that there doesn't seem to be much of a downside unless I'm missing something obvious.
It's also a bit self-documenting which is nice.