Why should I use Google's CDN for jQuery?

Question

This may be obvious to some, but I\'ve been wondering: why should I depend on Google\'s server to host jQuery for my site?

Is it only because it loads faster this wa

Answer 1

This study by TJ VanToll convinced me that it's better to concatenate jQuery with other scripts rather than load it from a CDN.

The reason is the latency involved in fetching jQuery on mobile devices:

"In 2012 the average RTT time on a mobile network in the United States was 344ms. And that 344ms applies to not only every HTTP request – which the average web page now makes 93 of – but also every DNS lookup and TCP connection... While average RTTs are improving, there are only small additional gains to be had, as current networks are within a small factor of the theoretical limit dictated by physics."

He also cites this post from Steve Souders that shows why you're actually unlikely to get the caching benefit from using a CDN:

"Because of the fragmentation in CDN providers, jQuery versions, and protocol usage (http vs. https), the chances of getting a CDN cache hit are shockingly low – and downloading from an external domain has the potential to perform not one, but three round trips (a DNS lookup, a TCP connection, and an HTTP GET)."