Jeff King from the Web Tools team wrote up a great post earlier this week that answers a number of common questions about how JavaScript intellisense works with VS 2008. I highly recommend reading it.

One trick he talks about which I'll show here is a technique you can use when you want to have JavaScript intellisense work within user-controls/partials (.ascx files).  Often you don't want to include a JavaScript library <script src=""/> reference within these files, and instead have this live on the master page or content page the user control is used within.  The problem of course when you do this is that by default VS has no way of knowing that this script is available within the user control - and so won't provide intellisense of it for you.

One way you can enable this is by adding the <script src=""/> element to your user control, but then surround it with a server-side <% if %> block that always evaluates to false at runtime:

Figure 10

At runtime ASP.NET will never render this script tag (since it is wrapped in an if block that is always false).  However, VS will evaluate the <script/> tag and provide intellisense for it within the user-control.  A useful technique to use for scenarios like the user control one.  Jeff has even more details in his FAQ post as well as his original jQuery intellisense post.  Rick Strahl also has a good post about using jQuery intellisense here.