It's common to separate content from design or markup from inline style.
.show() and .hide() are using inline styling which is also part of the
markup in
https://github.com/apache/couchdb/blob/0af1b0959d13641c1e0d9c7e032098914581735e/src/fauxton/app/addons/config/templates/item.html#L25

You don't want to use JavaScript to style a webpage, that is what CSS is
made for. There are alot of reasons against inline-styles, e.g.:

 - Consistency,
 - Separation of Concerns

But if you are interested, you can google alot more about the topic!