In VS2013 RTM, we shipped a not well known feature for _references.js file: /// <autosync enabled="true" />.
For example, create a new MVC project, open scripts/_references.js file and you will see the following if you are using VS2013 with update 3.
Drag and drop bootstrap.js file to the Scripts folder to make a copy, and all the missing “.js” files and the newly added “.js” files are automatically referenced in the _references.js file. Note, we ignore the “.min.js” files if the non-minified “.js” file exists.
For more details in _references.js, please visit Mads’ blog The story behind _references.js.