Page Speed: Serve resources from a consistent URL

Page Speed recommends:

Serve shared resources from a consistent URL across all pages in a site

For resources that are shared across multiple pages, make sure that each reference to the same resource uses an identical URL. If a resource is shared by multiple pages/sites that link to each other, but are hosted on different domains or hostnames, it's better to serve the file from a single hostname than to re-serve it from the hostname of each parent document. In this case, the caching benefits may outweigh the DNS lookup overhead. For example, if both mysite.example.com and yoursite.example.com use the same JS file, and mysite.example.com links to yoursite.example.com (which will require a DNS lookup anyway), it makes sense to just serve the JS file from mysite.example.com. In this way, the file is likely to already be in the browser cache when the user goes to yoursite.example.com.

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