Enabling javascript intellisense for external libraries in Visual Studio

I updated ~/Scripts/_references.js with

/// <autosync enabled="true" />
/// <reference path="angular.js" />
/// <reference path="angular-route.js" />

and in my app.js I can see some intellisense working, which is great

but go a little further and it doesn't work anymore.

Any ideas on why this happens or ways to make it work?