I started a joke project to mock the total mess that jQuery has become, http://cowbelljs.com/ . The performance hit from using jQuery is awful these days, it's become a monolithic framework aimed towards support for a hodge-podge of things rather than using best practices.
A simple line of code such as this might be readable:
$(".foo input[type=checkbox]:checked").live(function(e){fizzbuzz(e)})
But, the costs of that? You've just killed performance, your page is probably going to have laggy response and all kinds of event listener issues crop up as you keep working, leading to you using .die, .stopeventpropegation, .stopeventbubbeling, and return false all over the place in a futile attempt to manage your events.
jQuery does a great job of letting you write less code, it also does a good job of abstracting away tasks and making things look like "magic", but it also really makes it easy to shoot yourself in the foot, with a tommy gun.
jQuery creates a lot of undesirable effects, as far as I'm concerned:
- People don't understand what their code does.
- jQuery API is a mess, and version upgrades are hard
- Best practices for a given task are not focused on, rather, "every practice" is accepted, and whatever blog post the JS novice read at the time becomes the method they write their code with (as a result, we almost never see .delegate() in use)
- The library is huge. Yes, they brag about it being only 31kb minified, but that's huge!
- jQuery code is slow.
- Nobody understands how the DOM API works any more, and because sizzle makes it easy to select complex things the authors don't even bother writing semantic HTML, so we start to see <td id="Row2Cell2"> kind of things.
- We have landed in a mess where ambitious people tightly couple their projects with an unstable API and practices that create sluggish pages.
Sure, you can use jQuery correctly, but I'd rather use a micro-framework that complements JavaScript rather than attempt to replace it with tightly-coupled abstraction layers and memory hogging through event listeners and timers all over the place. The culture around it makes me really sad.