run function on editor right (components) panel update

I want to change slightly content of excerpt component panel (i want to add a counter). It works by simply adding a script to the post.php page. But when I then click e.g. to editor, than the right panel switch from Post to Block and when I go back to Post panel, it is whole reinitialised so again without my changes.
Is there any way how can i run my script always when that component panel is generated? (e.g. catch some event)
thanks

• This topic was modified 1 year, 7 months ago by Jan Dembowski.