A pattern that should work is to have an actual class for each event. For example, shaka.Player.ErrorEvent = class { ... }

The constructor takes all the necessary parameters, like the error object (shaka.util.Error), but the constructor would hard-code the type constant (like "error"). These would all inherit from shaka.util.FakeEvent.

So instead of the player calling this very generic utility for constructing FakeEvent instances:

const event = shaka.Player.makeEvent_(
    shaka.util.FakeEvent.EventName.Error,
    (new Map()).set('detail', error));

you would simply call the constructor for that specific event type:

const event = new shaka.Player.ErrorEvent(error);

This is much cleaner, and the types would be automatically documented.