VS 2008 JavaScript Debugging

A few weeks ago I blogged about the new JavaScript Intellisense support in VS 2008.

One of the other JavaScript features that I'm sure will be popular in VS 2008 is the much-improved support for JavaScript debugging.  This is enabled in both the free Visual Web Developer 2008 Express edition as well as in Visual Studio, and makes using JavaScript and building AJAX applications significantly easier.

Setting JavaScript breakpoints in ASP.NET pages

One of the annoying things with VS 2005 is that you have to first run your ASP.NET pages before you can set JavaScript breakpoints in them in the debugger.  

VS 2008 makes this much better by adding new support that allows you to set client-side JavaScript breakpoints directly within your server-side .aspx and .master source files:

When you set a breakpoint in your .aspx page like above, VS 2008 will automatically map the breakpoint location to the dynamically generated client HTML that runs in the browser when the page is later executed:

If you add/remove/update the breakpoint locations in the running HTML document, VS 2008 is also now smart enough to perform the reverse mapping and update the breakpoint in the original .aspx or .master source file on the server.  This makes it much easier to get into a nice edit/debug/edit/debug flow as you are iterating on your applications.

Best of all, you can now set both client-side JavaScript breakpoints and VB/C# server-side breakpoints at the same time (even in the same page) and use a single debugger to step through both the server-side and client-side code in a single debug session (which is extremely useful for any AJAX heavy application).

Any JavaScript breakpoints you set will also now by default be saved by VS 2008 when you close the project/solution.  When you open up the project again, the previous locations you set the breakpoints on will still have them enabled. 

Script Document Navigation within the Solution Explorer

Often the JavaScript that is sent down to a browser client is dynamically generated on the server (for example: with scripts that are stored as resources within compiled server controls - like ASP.NET AJAX UpdatePanels and control extenders).  In scenarios such as these, you want to be able to easily see all JavaScript URLs being loaded from a page, as well as step into the within the debugger.

VS 2008 makes it much easier to-do this by integrating the running Script Document feature (that in VS 2005 was a separate tool-pane window) into the VS 2008 solution explorer view when you are debugging a web application. 

Specifically, when you are using VS to run and debug a page, VS 2008 will now list all of the script URLs that the page you are debugging has loaded in the browser at the top of your VS solution explorer pane:

You can then double click on any of the URLs under the "Script Documents" node at the top to see the JavaScript file that was loaded in the page:

You can obviously then set breakpoints in the loaded JavaScript and debug everything. 

Much Richer Debug Watch/Locals and Visualizer Support

Easily opening and navigating JavaScript files in the debugger is nice - but the real meat of the improvements made with VS 2008 JavaScript debugging is in the much improved object execution and inspection support.  When you inspect a variable within the debugger using VS 2008, you'll find much more detailed object information is now available:

You can now browse runtime object methods:

You can now browse runtime object events:

And you now get much, much more detailed property and property type information of running objects.  Note below how I am traversing the div element's "parentElement" property to dynamically look up details about the element's parent HTML element and overall position within the HTML DOM:

You can obviously use the debugger property grid above to both lookup as well as set values.  You can also run code in the immediate window to retrieve and change JavaScript at runtime:

VS 2008 also provides support for pluggable debug visualizers that you can use with JavaScript debugging.  This enables developers to add extensions to the debugger that can work against running objects and provide richer visualization views of them.  For example, we could use the built-in "Text", "XML", or "HTML" visualizer to load a dialog to better inspect a value:

I suspect we might see a cool CodePlex project providing nice JSON and REST JavaScript visualizers soon. 


The above walkthrough hopefully provided a good overview of some of the new JavaScript debugging features coming soon.  There are many more JavaScript and AJAX features coming in VS 2008 and .NET 3.5 that I'll be covering in future blog posts. 

Note that because of the new VS 2008 multi-targeting support, you can use the JavaScript debugging features above with both ASP.NET applications built using .NET 3.5 (which also now has ASP.NET AJAX built-in), as well as with existing ASP.NET 2.0 applications (including ones that use the separate ASP.NET AJAX 1.0 download). This, combined with the new VS 2008 JavaScript intellisense support, provides a very compelling reason to start using VS 2008 - even if you are using it to only target .NET 2.0 applications.

Hope this helps,


P.S. To learn more about VS 2005 JavaScript Debugging, please read this blog post.  Dan Wahlin also recently posted a nice set of AJAX testing and debugging tools that I recommend checking out here.


  • Hi Tom,

    >>>>> When will the Beta 2 bits be available?

    The good news is that Beta2 is less than a week away.... ;-)



  • Hi Maulik ,

    >>>>>>>> I'd like to drag your attention to one point that I tried to remove the break point at runtime (I use BETA 1) but it didnt let me remove it. Does it allow in BETA 2??

    That is odd - did you press F9 on the line to toggle the breakpoint? That should always work.



  • Hi Zeeshan,

    >>>>>> Scott, Can i open up asp.net 2.0 project in VS 2008 and then be able to open up in vs 2005. cuz i would really like to go ahead and start using the product with go live license. however many developers in my company wont be willing to do that. It would be nice for me to be able to open the same project from source safe using VS 2008 check in my stuff. and others can check out using vs 2005.

    The project file format can be used with both VS 2005 and VS 2008 as long as you copy the targets file onto machines that don't have VS 2008 installed (this is an XML file with manifest definitions).

    However, the .SLN solution file is version specific - which means you you can't open a VS 2008 .SLN file that points to projects with VS 2005. You'd need to maintain two .SLN files - one for VS 2005 and one for VS 2008 if you want to swap projects back and forth between them.

    Hope this helps,


  • Hi Ken,

    >>>>>> The intellisense is awesome but a bit intrusive. Is there a way to set it to match case as well? Our Javascript objects often have properties that match intellisense properties somewhat. For example obj.Val or obj.Value require you to hit escape to lose the intellisense box or obj.valueOf will be automatically chosen. If the box would only show up with a case match that would save a lot of hits to the escape key. If you use a Microsoft Natural Ergonomic Keyboard you know how annoying reaching for that escape key can be.

    I believe the JavaScript intellisense is case sensitive. If you want to email me a sample of a page you are having problems with, I'd be happy to loop you in with the team for them to test it.



  • Hi Ben,

    >>>> Hi Scott; An OT question: a) Will there be a newer version of SilverLight SDK 1.1 along the next version of VS2008 Beta 2?

    Yes - our plan is to have an updated Silverlight 1.1 SDK in the next week. It will work with VS 2008 Beta2.

    >>>> b) Will there be design-time support for SilverLight 1.1 and WPF in Beta 2? Thanks!

    VS 2008 Beta2 ships with a built-in WPF designer and project system support. I think you'll find it is a pretty good way to start developing WPF applications.

    Silverlight 1.1 support within VS 2008 will be provided by a separate Silverlight SDK download that you install on top of VS 2008.

    Hope this helps,


  • Hi Ben,

    >>>>>> On the second note, I was reading an article last night about iPhone and it said, iPhone's biggest strength isn't it's phone, but rather it's wireless browser. Since the device is running on Mac OS X, do you think MS is planning to support this device with SilverLight? This is the only portable device I've seen, that has usable screen and processing power.

    I'd like to support Silverlight on the iPhone - but right now Apple is not allowing third party software to be installed on the device. So we'll have to see whether this changes in the future.



  • Hi Ben,

    >>>>>> My question to you is, are there any guidelines as to what 1.1 can do and what it can't do? This way we can create a strategy up front what parts of project we should do in ASP.Net and what parts in SilverLight, before we find out in a hard way. I think in one of your blogs, it would be helpful to have a functional list.

    I'm planning on covering this more in the future with some blog posts. Right now the V1.1 functionality is still limited for data entry scenarios (no textbox, no core set of controls, and no databinding) which makes it very hard to build data entry LOB applications using it. This will change in the future as though features come online.

    >>>>>> Secondly, I've been asked whether SilverLight will run on Windows2000. Seems like many people are still running machines with Win2K.

    Right now our plan is to support Windows 2000 as well with Silverlight in the future.

    Hope this helps,


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