Enable javascript syntax highlighting for Visual Studio 2012 / intellisense for custom file extension

Question

I am working on a project that uses javascript in some files that have custom file extensions (.js.template). I would like to use the code completion / highlighting that Visual Studio attaches when editing these files, but there seems to be no way to apply Javascript editing to files that do not end in .js.

I tried Tools -> Options -> Text Editor -> File Extension , and then added the extension to the template and assigned it to various available editors (including the Script Editor and HTML Editor), but this does not seem to mean that any Javascript code is highlighted or intellisense. There seems to be no Javascript Editor.

I am using Visual Studio 2012 Express

Any ideas?