Use a relative URL for JavaScript, CSS & Images

A relative URL without a scheme is perfectly valid.

<script src="//www.example.com/script.js"></script>

<link href="//www.example.com/style.css" rel="stylesheet" type="text/css" />

<img alt="" src="//www.example.com/image.png" />

https://www.example.com:8080/some/resource?key=value#hash
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scheme        host      port      path       query   fragment