One of the points the post makes is that by that time, making changes is a lot harder than it would have been if one had just started out with the proposed setup.

I'm not sure this qualifies as premature optimization. Allowing jQuery to block page load incurs a bit of load time where the user has to sit around waiting. Anything that can be done to minimize user frustration (and maximize user experience) is probably worth doing when it's so simple.

Agreed. Premature optimization is about "maybe", and feared performance loss.

Responsiveness matters to users; to them, speed is a feature, insofar as they can perceive it. The "JQuery tax" absolutely is a real, and user-perceptible issue.

"Avoiding premature optimization" can sometimes make it hard to undo poor design choices made early on that could have been avoided.

> Responsiveness matters to users; to them, speed is a feature, insofar as they can perceive it. The "JQuery tax" absolutely is a real, and user-perceptible issue.

I think the evil of premature optimization is attacking the wrong target first. 80ms isn't a small amount, but moving script tags around could have more potential side effects than say using proper caching, minifying etc

Good point. This hadn't even occurred to me.

After the initial load from the CDN the tax is 10ms (Chrome), 20ms (IE9) or 80ms (Firefox). So for modern browsers it's really a tiny amount you save. For IE7 users the tax is more than 100ms but it seems a waste of time to optimize for them given their market share.

I'd say saving 20ms is premature unless you are already doing everything else you can do.

I would tend to agree with the other commenters and say, why not just put it at the bottom in the first place? That way, you design the whole site with jQuery loading last and, hence, you never have a massive headache trying to change it!

This is not premature optimization. It's about not making spaghetti code (HTML/CSS/JS in this case). Have clear guidelines from the start, that's it. No optimizations. In fact having clean code makes development easier (this applies to webdev too). If the framework you picked makes it harder, ditch the framework.