Author makes some points that are fine, I guess. A dev needs to carefully consider his audience and his fellow developers. If I can use jQuery and know that I'm not going to have cross-browser DOM API issues, then let me have it. Because the method simply doesn't work in older browsers (<IE8 http://caniuse.com/#search=queryselectorall) It's not entirely fair to say that `$(".my-class li:first-child")` is equal to `document.querySelectorAll(".my-class li:first-child")` or that `$('.my-class')` is equivalent to `document.getElementsByClassName('my-class')` (doesn't work in <IE9 http://caniuse.com/#search=getelementsbyclassname).

If you're building games or working with a team who does, I'm going to guess you're working with fairly edge functionality in browsers where javascript support is great. If you're building sites for clients who are still (sigh) using IE7 internally, you just can't get away with something quite so simple.

As another commenter mentioned: "Even the most avid follower of JS updates can't compete with a team of the standard jQuery draws upon. When a new method gets rolled in to the core of jQuery, something that speeds up selectors for example, your code improves without you doing any work."

This is the same reason I use a library for preprocessing my CSS. I'd rather update a gem and trust a team whose focus is processing CSS than try to rely on myself for keeping up to date with the pace of the CSS WG and browser vendors.

Also, for anyone wanting to dig around the jQuery source, James Padolsey made a great tool for it. I know I was pretty amazed to find out just how much is going on under the hood. http://james.padolsey.com/jquery/#v=git&fn=