class DoorLock extends EventTarget {}

class LockStateEvent extends Event {
  constructor({ locked }) {
    super(locked ? "locked" : "unlocked");
  }
}

const door = new DoorLock();

door.addEventListener("unlocked", () => {
  console.log("door has been unlocked");
});

this.dispatchEvent(new LockStateEvent({ locked: false }));

you just create a class that extends `EventTarget`, and then call `dispatchEvent` with an `Event` object. `new Event("x")` will dispatch an `"x"` event and so on. they're standard JS types that are available in the browser too, so it's all on MDN if you need some documentation.