Custom events in jQuery are super simple, and really neat to use.  Unless and until a javascript framework like this ends up in core, they are probably the best way to allow for a nice degree of extensibility in your javascript for other developers.

For the 3.8.11 release of WP eCommerce, we did a massive overhaul of our JavaScript.  To give an idea of the scope, we ended up removing 20,000 lines of code.  That’s right, bold and italicized – it was that awesome.

One of the elements we added were a few custom events.  For example, we had a particularly nasty action hook in our add_to_cart() function.  It essentially encouraged developers to hook in and echo out some eval()’d javascript, so that when something was added to the cart, they could override our default javascript mechanism that does, well, stuff.

Not only is this equally insecure and lame – it’s actually a fantastic use case for a custom event.  Rather than insecurely eval()ing javascript here like we were before*, we have a sexy new custom event for plugins to use.  Here’s a really basic overview of how you might use it.  As a plugin author or theme author, you’d likely put the following code in a javascript file, properly enqueued and such.  For my example, I’m just outputting it to wp_head.  For an exercise in futility, check out our veritably imperfect attempt at backwards compatibility.

And voila, lovely custom JS events for everyone.  A fantastic and incredibly useful development concept.