问题
I have been looking at the html5 boilerplate and noticed that the jquery include url starts with a double slash. The url is //ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js
Why is the http: missing?
回答1:
I hate answering with a link but this explains it - http://paulirish.com/2010/the-protocol-relative-url/
Using a protocol relative URL like "//mydomain/myresource" will ensure that the content will be served via the same scheme as the hosting page. It can make testing a bit more awkward if you ever use FILE:// and then some remote locations as they will obviously resolve back to FILE. Never the less it does resolve the mixed insecure/secure content messages you can cause by not using it.
回答2:
So that if the .html is accessed via HTTPS; the page will not have any unsecured script.
来源：https://stackoverflow.com/questions/6350244/double-slash-at-beginning-of-javascript-include