JavaScript, Web

Logging JavaScript exceptions. Custom solution + ELMAH

Development team was reported about critical bug in production. First thing they did was checking server logs but they were empty. Impossible! On the other hand the client sent screenshot with error alert.
Have you ever experienced such scenario? It happened to me many times. And it’s nothing extraordinary – the more code on the client, the more probable to commit a bug. The worst thing is that’s so hard to track such bugs. After all it came out that’s not that hard. Here’s my solution:

  1. (Optional but recommended: use ELMAH. It adds a nice error log and page to browse already caught errors + some extra information about context of such errors)
        Install-package elmah
    or if using ASP.NET MVC
        Install-package elmah.mvc
  2. Listen for client-side errors and send them to the server (custom errorLogging.js script):
    Please note, that the code above does not work on IE7 and below (just to keep it simple). IE supports JavaScript stacktrace from version 10+ that’s why there is “if” clause between lines 16-18.
  3. Add back-end code to listen for exception logsjserror4
    You could use MVC or WebAPI controller, but handlers feels more like infrastructure. If you don’t want to use ELMAH, then replace line 36 with your logging mechanism (or “throw jsException“).
  4. Create exception type specific to JavaScriptjserror5
    It’s particularly important to override ToString() method as it’s used by ELMAH to dump exception details.
  5. Connect it all together: add script reference to errorLogging.js and register JavaScriptErrorHandler class in global.asax.cs

And there it is! If you don’t want to do it yourself go to my github page and download a working sample: Blog.ClientSideExceptionCatching

After playing for some time here are the results. As you can see both server-side and client-side errors are kept together with the time they occurred.
If you go deeper then you see exception details (message, stacktrace).



This is something that we get by our hands. Elmah also gives us a very useful gift as it logs all server variables, including HTTP_USER_AGENT that tells us what browser was used on the client. You don’t need to ask the user for such things. Handy!

Off-topic/final points

  • First I tried jsnlog but failed. It forced me to use Common.Logging and was not working out-of-the-box.
  • Beware of Internet Explorer – it generates localized exception messages (see the first elmah screenshot) and may not support stack trace
Refactoring, tools, Web

Removing unused UserControls with NDepend


NDepend is an amazing analysis tool for .NET code. It gives you deep insight into your code and let you manage its quality easier. It lets the user execute LINQ queries on code, generates dependency graphs, metric view, check rules and many many more. In this post I’ll show a very simple trick to detect unused user controls that can be removed from our project.

NDepend was recommended by Scott Hanselman, Greg Young and others. I tried it some time ago in my small project but I couldn’t benefit from the tool. After some time I had to do some cleaning in our legacy system. Then I came back to the the tool and I have to admit that I fell in love with it.

Some time ago I wrote about Finding unused private and public methods with Resharper. It is of course very nice way of doing code clean-up but in rather smaller systems. In my case Resharper found around 2.5 thousand issues and it’s not an amount that I could face in one or two iterations.

Some issues are specific to particular parts of the solution. In WebForms project the highest level of abstraction is Page and Control. If the user removes/refactors page and decide to not use some user control it becomes dead source of other dependencies.

In the first iteration I decided to get rid of unused pages with help of google analytics report from the last few month. The next one was about dead user controls. Resharper doesn’t allow us to find unused types deriving from specific base type. Here is the place for NDepend.

In “Queries and Rules” section I run the following query:


As a result I got the list of around 30 user controls. Unfortunately this is just an input for further filtering because it lists controls that are not used in code, but not saying anything about markup. All in all checking this is not that hard, one solution is to go through all of them and check what compiler says or find all occurences of “<%@ Register Src="~/Path/MyUserControl.ascx" TagPrefix="uc" TagName="MyControl" %>” for each *.ascx file.

Portfolio, Semantic Web, tools

RDFCommander beta released



RDFCommander is a small tool to browse linked data (triples) using SPARQL Endpoints. It’s main goal is to be useful staying easy & intuitive as Total Commander. I wrote it to help me with debugging/discovering data from remote endpoints.









To connect you need to click: File –> Connect option or the “earth’ toolbar button. Then you need to select SPARQL endpoint (default is and initial Node URI. After successful connection you should see the data loaded into the main view. You can navigate using arrow keys (Up, Down). You can enter node using ENTER key. You can also navigate back with BACKSPACE or “Back” button.



View mode

Triples are presented in two modes: “Node as subject” or “Node as object”. That’s why there are only two parts of the triple visible at the same time (the third one is constant while navigating and there’s no need to show it in the list). The default view is “Node as subject” In this view the SPARQL endpoint is queried about all the triples with Subject set as the given node. You can change the view using “Swap view” command (or the toolbar button):


In “Node as object” view it loads all the triples with Object set as the given node (as shown below):




You can download the app here: RDFCommander
Keep in mind that it is still beta so it’s not bug-free yet. You can request issues/report bugs using project’s issue tracker: