jQuery is a bloated library that tries to do too much. It's slow and becoming less and less necessary as browsers become more standards compliant.

Can you link to articles on jQuery's performance issues?

Is it's implementation slow, or do you mean it's size makes over the wire transmission slow?

Are all jQuery methods slow, or specific cases like DOM manipulation and/or AJAX calls.

It seems that a few years back jQuery had these issues, but are those claims still relevant?

It's because jQuery is a library on top of JavaScript. That makes it slower than native JavaScript.

If you don't need to support very old browsers you can easy go without jQuery.

Have a look at http://youmightnotneedjquery.com

Also: http://ponyfoo.com/articles/why-i-write-plain-javascript-mod...