We\'re beginning work on a couple of fully JavaScript-dependent web apps (our previous apps have been ASP.NET MVC, with JavaScript \'goodness\' sprinkled over-the-top).
great question, I've been thinking about this for quite some time. The only solutions that have popped up in my mind are hosting the files on the web and using them like a cdn or using symlinks. You could add a code snippet into your visual studio to reference them.
In the end, this is how I've achieved it. It may not be to everyone's taste - but worked a treat for me.
Note: In all of our projects, static resources are in a root directory called 'Assets', so for example JavaScript is always in /Assets/js/ and CSS /Assets/css/.
Solution
When the project builds, it copies the imported files to \bin\Assets\js - the post-build event then takes a copy of those over to the project directory - in time for the site to use them.
Use proper version control.
Keep the js in one location and then just git pull
(or the equivelant Mercurial / Bazaar) them back into your code whenever you've updated your javascript.
Anyone that stumbles across this question here in the future should know that there are now Shared Projects in Visual Studio to solve this problem. Universal Windows projects use them by default and you can create your own by downloading and installing the VS extension here: https://visualstudiogallery.msdn.microsoft.com/315c13a7-2787-4f57-bdf7-adae6ed54450
Once you download the extension you can add a Shared Project (Empty) to your solution. The project can be found in the project templates for Visual C#, Visual C++, and JavaScript.
Then include the files you want to share to the shared project in any folder structure that makes sense for you.
Next you will include the shared project as a shared reference in the other projects in that solution that need access to the shared files. Right-click the other project and choose "Add Shared Project Reference".
Now you can reference the shared files in your main project as if the files in the shared project existed there. They are compiled as part of that project.
The technology was intended for Universal apps to share code between Windows Phone and Windows Store apps so be warned that you may have trouble sharing in different scenarios but it is worth a try to see if it will fill your need.
You could perhaps use visual studio templates
I know this issue is ancient, but still wanted to put forward my solution because it is a bit simpler than beardtwizzle's.
You can ensure that Visual Studio copies all linked files to where you placed the link in Visual Studio's Solution Explorer by adding this at the end of your .csproj file:
<Target Name="CopyLinkedContentFiles" BeforeTargets="Build">
<Copy SourceFiles="%(Content.Identity)"
DestinationFiles="%(Content.Link)"
SkipUnchangedFiles='true'
OverwriteReadOnlyFiles='true'
Condition="'%(Content.Link)' != ''" />
</Target>
I've described how this works in my blog post at http://mattperdeck.com/post/Copying-linked-content-files-at-each-build-using-MSBuild.aspx