Hello

PS: ist it really necessary to keep a separate JS-ressource for only the one event listener?

No, it isn't. We can also remove the files and modify the main.(min).js as well

 document.addEventListener("DOMContentLoaded", function(e) {
var mlf = new MyLittleJavaScript();
var ajaxPreviewStructure = typeof settings != "undefined" && typeof settings["ajaxPreviewStructure"] == "string"?settings["ajaxPreviewStructure"]:false;
if (mlf && typeof lang == "object") 
mlf.init(ajaxPreviewStructure);
new DragAndDropTable(document.getElementById("sortable"), "bookmarks", "mode", "admin", "action");
});

To answer in an emoji-like manner:

Tschö, Auge