> And by going that route you make sure that all pieces of your website have the same availability guarantees, the same performance profile, and the same security guarantees that the content was not manipulated by a 3rd party.
You can already guarantee the security of the file by using the integrity attribute on the <script> tag. And the performance of your CDN is probably worse than the Google CDN (not to mention that you lose out on the shared cache).
I agree on the security side if you use that attribute. However:
> And the performance of your CDN is probably worse than the Google CDN
What means probably? Other CDNs (Akamai, CloudFront, Cloudflare, etc) are also fast.
And by pushing one piece of your website on a different CDN you force your users browser to create an additional HTTPS connection which takes additional round-trips, instead of being able to leverage one connection for all assets. This alone might as well outweigh the performance differences between CDNs.
Also the "shared cache" benefit might go away, if I read the other answers in this topic correctly.
You can already guarantee the security of the file by using the integrity attribute on the <script> tag. And the performance of your CDN is probably worse than the Google CDN (not to mention that you lose out on the shared cache).