How do I link scripts externally and internally?

I have a website that I want to work online and offline. I want to decrease load time, so I minified the slow loading scripts. It didn't work enough. Locally, some of the scripts are taking 4-6 seconds to load.

I know that linking scripts externally speeds it up drastically. I have tried it and it works. But some of the users will not have internet access. Is there a way to link a group of scripts to an external site, and locally if they do not have internet access?

 <script src="js/jquery-1.9.1.min.js" type="text/javascript"></script>
 <script src="js/jquery.dataTables.min.js" type="text/javascript"></script>
 <script src="ui/jquery-ui.min.js" type="text/javascript"></script>