Listeners and Emitters
Sometimes the same object will emit multiple types of events with different names. For example, a button might emit both a
Objects that emit multiple events are often implemented using an event emitter class (either built-in or from a library).
We typically call event handler functions event listeners when they handle (or listen for) named events.
Listeners are common when handling user input.
In the browser, for example, buttons emit a
"click" event, and we can use
addEventListener to handle it.
Some environments like
node.js and React Native come with a built-in event emitter class.
Here's how a custom one might be implemented.
Event emitters don't fundamentally have to interact with the event loop — handlers can be called synchronously too. However, using the event emitter pattern doesn't make as much sense in this case.