I have a web page copy of a bootstrap official demo/template page. Bootstrap needs JQuery. I know this. The template already has a link to the JQuery page.
However, in my page the NavBar menu is not working unless I add a second link to JQuery:
A more specific answer If I may.
An answer like "you need jquery for bootstrap" isn't fully right cause you can still use it without JS but there are several features that require js/jquery.
According to the manual, the Navbar feature has dependency in jQuery, as follows:
The responsive navbar requires the collapse plugin to be included in your version of Bootstrap.
So if you want your navbar to be responsive (= collapse) you need to include that collapse js plugin which depends on jQuery library.
In the original template the jquery script is being included. Just instead of a CDN file (from google's library) it's a local copy of an old version.
Please notice that different versions of bootstrap requires different versions of jQuery. So a newer version of bootstrap might require a newer version of jQuery.