CODEWITHSUNDEEP
javascripthtmlwebsrc
Macklin
Macklin

Reputation: 177

How does HTML load external JS files

I'm a beginner in web dev and I've recently come across some code that includes two external JS files in the following way: 

<script src="//code.jquery.com/jquery-1.12.0.min.js"></script>
<script src="//d3js.org/d3.v3.min.js" charset="utf-8"></script>

I know the browser will perform additional HTTP-requests to get the referenced files. Now, this is what's got me wondering:

When I put the containing HTML-file into the XAMPP htdocs folder and access it via localhost, everything works fine. However, when I just open the local .html-file in Chrome oder Firefox, it won't be able to find these external JavaScripts.

Obviously, this isn't a problem, since you wouldn't normally use an HTML-file that way, but I still wonder what happens here. Does it need some kind of server to include external JS files? Interestingly, it works when I include the files like this:

<script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>

It would be really interesting to know why =)

Cheers!

Upvotes: 0

Views: 742

Answers (2)

Jose Zamudio
Jose Zamudio

Reputation: 865

<script src="//code.jquery.com/jquery-1.12.0.min.js"></script> is using a relative url, it will use the protocol scheme from the displayed page, but against the host in the URL. On an HTTPS page, this will be an HTTPS request, on an HTTP page, it will be an HTTP request.

So in other words it will look for the correct protocol - HTTP or HTTPS - used by the requested page and use that.

Here is a good read about this topic: http://nedbatchelder.com/blog/200710/httphttps_transitions_and_relative_urls.html

Upvotes: 1

Ismail Farooq
Ismail Farooq

Reputation: 6827

localhost has http:// protocol if you copy your localhost url and paste it to any editor u can simply see the http:// with your localhost url but when you directly open file via file:// it doesn't, that's why your files were loaded when you access via XAMPP localhost.

Upvotes: 1

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