on() / off() sketch.

gistfile1.txt

Using some experimental JS IDL syntax:

augment EventTarget {
  EventTarget on(String type, EventListener callback, 
    {boolean ignoreBubbles?, 
     String? filter = null, 
     enum("capturing", "target", "bubbling") phase = "bubbling",
     String? marker = null});
  EventTarget off(String type, EventListener callback);
  EventTarget off({ String? type = null, String? marker = null });
}

filter takes a selector. When filter is supplied ignoreBubbles defaults to true 
which means the Event.bubbles property is ignored during event dispatch making 
event delegation work better.

marker can be used for namespacing. E.g. to remove all event listeners at once
registered for the "button" component.

Everything else is as you expect it.

Lovely. Any update on when can we have this?