You can use a CDN and still have Intellisense support in Visual Studio. There are two ways to do this:
Add an Intellisense reference to the *vsdoc.js
file that is hosted
on the CDN. Go to Tools | Options
:

Note that you will need to make an entry for each *vsdoc.js
that
you want to use.
- If you know that the
*vsdoc.js
file is co-located in the same directory with the js
file on the CDN (like it is on the ASP.NET CDN), AND you're using MVC, you can just update your _references.js
file to reflect this:
/// <reference path="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.10.0.js" />
If you need help with _references.js, see my blog entry here.
Be sure to update your webpage (or _Layout.cshtml) reference to actually use the CDN too. Note that the js
path that you use for your web pages doesn't have to be the same as your Intellisense reference (of course, you obviously want them to be the same version)!
<!DOCTYPE html>
<html>
<head>
<title>@ViewBag.Title</title>
</head>
<body>
<div id="body">
@RenderBody()
</div>
<script src="@Url.Content("http://ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.js")" type="text/javascript"></script>
@RenderSection("scripts")
</body>
</html>
NOTE: The examples above assume that you're not using ASP.NET 4.5 bundling, or taking advantage of CDN features such as path mirroring and reverse proxies. I assume that if you're using these features, you know what needs to be done to get them running.