Out of sight, not out of mind.
While extending some jQuery functionality on a page, I noted that a form element's "change" handler wasn't being invoked, which meant some of the page initialization code would be left out. So I helpfully added it:
What I failed to contemplate was how this would impact another page, which just happened to have some (but not all) of the same form elements, and referenced the same JS code at page load. Specifically, my page's sibling had:
<input name="foobar" type="hidden">
And of course this broke in production.
Well, that's interesting. A change handler on a hidden form input field isn't usually all that useful, so I figured out I really needed:
It happens that the ".filter()" step is actually more efficient than doing it all in one selector ("input[name=foobar]:visible"), because of some obscurities within jQuery. That little discovery was of value to an End Point co-worker, who realized she could shave a little time off a page load elsewhere, so my minor page malfunction will redeem itself.