Preconnect/dns-prefetch resource hint against web.dev best practices
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schlessera commented
I think this combined preconnect and dns-prefetch resource hint is not always doing what it is supposed to do depending on the browser:
As far as I can tell, the dns-prefetch is meant to be the fallback in case the preconnect is not supported (as the preconnect would include a DNS resolution). However, the dns-prefetch is mentioned first, which seems odd.
Also, according to web.dev, best practice is to use two separate hints with the dns-prefetch as the second hint serving as a fallback, as using a combined hint will break in Safari:
https://web.dev/preconnect-and-dns-prefetch/#resolve-domain-name-early-with-reldns-prefetch
schlessera commented
Related issue in Go optimizer: ampproject/amppackager#489