preconnect relationship is similar to
dns-prefetch in that it will resolve the DNS. However, it will also make the TCP handshake, and optional TLS negotiation.
This is an experimental feature.
<link rel="preconnect" href="URL">
Informs browsers to resolve the DNS for a URL, so that all assets from that URL load faster.
<link rel="dns-prefetch" href="URL">
Informs the browsers that a given resource should be prefetched so it can be loaded more quickly.
<link rel="prefetch" href="URL">
DNS-Prefetch resolves only the domain name whereas prefetch downloads/stores the specified resources.
Informs browsers to fetch and render the URL in the background, so that they can be delivered to the user instantaneously as the user navigates to that URL. This is an experimental feature.
<link rel="prerender" href="URL">