If you come across an (older) application that is using Prototype Show archive.org snapshot instead of jQuery, you may often see events bound to single elements only, like this:
$('foo').observe('change', updateThings);
$('bar').observe('change', updateThings);
$('baz').observe('change', updateThings);
If you are calling only one method in each case, this is unnecessarily ugly. Also, when your page contents have been replaced via AJAX (like sections of a form after choosing something), those event hooks will no longer work.
Instead, just do it similar to what you know from jQuery:
document.on('change', '#foo, #bar, #baz', updateThings);
Or, just apply a nice data attribute to the form fields, and look for that in your JavaScript code:
document.on('change', '[data-requires-update]', updateThings);
If you are interested in the element that was triggered the event, simply take an event
argument and look at event.target
.