JavaScript Document Mutation Events

Sometimes you get a situation where you need to know when a new element has been added to the page with JavaScript. A common example of this is adding event listeners to a certain type of input then adding more of those inputs - the new ones do not get the event. For a simple example it's obviously easier just to add the event handler when adding the new input so let's assume we're talking about something more complex. There used to be an event for this kind of thing