addListener()

instance.addListener("foo", () => {
  /* [...] */
});

Parameters

Parameter	Type	Default	Description
event	string | symbol		The event name. Expects an ESMitterEventName.
fn	unknown		The function that will be called then the event is emitted.
context	unknown	undefined	The context to invoke the listener with.
once	boolean	false	Specify if the listener is a one-time listener.

on()

The on() method is almost an alias of addListener(), the only exception being the missing once parameter. For this, use once() instead.