Drupal 8: How to add custom control when editing content?

Question

Drupal

Good afternoon!
There are entities (Node) and there is a need for the administrator, in content editing mode, to add 1-2 buttons + text (not separate fields. Buttons are purely auxiliary).
How can this be done?
Ideally, for me, javascript will connect to the edit form.

Answer 1

via form alter.
and there already look at Drupal forms api, and connect the element. If you need to connect custom JS, then use drupal add js