C# 4 and .NET 4

What is ajax ❘ 1239
The code that achieves this is:
Sys.WebForms.PageRequestManager.getInstance().add_endRequest(
EndRequestHandler);
function EndRequestHandler(sender, args)
{
if (args.get_error() != undefined)
{
var errorMessage = args.get_error().message;
args.set_errorHandled(true);
$get('errorDisplay').innerHTML = errorMessage;
}
}
Note that the errorHandled property of the EndRequestEventArgs object is set to true. This prevents the
default behavior, which is to display the error message in a dialog box, by using the JavaScript alert() function.
The error itself is generated by throwing an exception on the server as follows:
protected void testErrorDisplay_Click(object sender, EventArgs e)
{
throw new ApplicationException(
"This is the message set in the exception on the server.");
}
There are many other situations when you will want to use event handling techniques to act on the
Application and PageRequestManager events.
Javascript Debugging
In the past, JavaScript has had a reputation of being difficult to debug. However, this has been addressed in
the latest version of Visual Studio. You can now add breakpoints and step through JavaScript code just like C#
code. You can also interrogate object state in break mode, change property values, and so on. The IntelliSense
that is available when you write JavaScript code is also vastly improved in the latest version of Visual Studio.
However, there will still be times when you will want to add debug and trace code to report information as
code is executed. For example, you might want to use the JavaScript alert() function to show information
in dialog boxes.
There are also some third-party tools that you can use to add a client-side UI for debugging. These include:
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Fiddler — This tool, which you can obtain from www.fiddlertool.com, enables you to log all HTTP
traffic between your computer and a web application — including partial-page postbacks. There are
also additional tools that you can use to look at what occurs during the processing of web pages in
more detail.
Nikhil’s Web Development Helper — This tool, available at http://projects.nikhilk.net/
WebDevHelper, can also log HTTP traffic. In addition, this tool contains a number of utilities specifically
aimed at ASP.NET and ASP.NET AJAX development, for example, the ability to examine view
state and to execute immediate JavaScript code. This latter feature is particularly useful to test objects
that you may have created on the client. The Web Development Helper also displays extended error
information when JavaScript errors occur, which makes it easier to track down bugs in JavaScript code.
The AJAX Library also provides the Sys.Debug class, which you can use to add some extra debugging features
to your application. One of the most useful features of this class is the Sys.Debug.traceDump() function, which
enables you to analyze objects. One way to use this function is to place a textarea control on your web page
with an id attribute of TraceConsole. Then, all output from Debug will be sent to this control. For example,
you can use the traceDump() method to output information about the Application object to the console:
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