There is a way to get ScriptEditor from EditorInterface by
var script_editor = get_editor_interface().get_script_editor()
script_editor has editor_script_changed signal, which is fired whenever the active script is changed (e. g. open a script, switch to another script etc), however I need a way to execute a function whenever the source code of a script is changed (e. g. a character inserted), it's not necessary to know what has been changed, just know that there's a change. Is there, may be, a signal for this? Thanks