When you use Ajax or Ajax related tools (such as AjaxControlToolkit) the browser sends aysnchronous request to the server which is of extension (.axd). The number of asynchronous requests in axd form, the more time it'll take to load the page. So if we can combine those axd requests into one then we can get noticeable improvement in page loading.
Figure 1: axd requests to the server
Here are the steps to combine axd scripts to a single on.
Register the dll in page:
@ Register Assembly="ScriptReferenceProfiler" Namespace="ScriptReferenceProfiler" TagPrefix="microsoft"
Add Control to the page:
<microsoft:ScriptReferenceProfiler ID="profiler1" runat="server" />
After adding the script profiler if you run the page then you will find all the script reference in your page as shown below. Remember you can't combine Microsoft provided js file like MicrosotAjax.js, MicrosoftAjaxWebform.js etc.
Figure 2: Script reference found by script profiler
2. Then use the scriptmanage's combinescript tag to combine script:
<asp:ScriptManager ID="sm1" runat="server" CompositeScript-ScriptMode="Release">
<asp:ScriptReference Name="AjaxControlToolkit.Compat.Timer.Timer.js" Assembly="AjaxControlToolkit, Version=3.0.20820.23813, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e" />
Assembly="AjaxControlToolkit, Version=3.0.20820.23813, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e" />
After combining those scripts you'll find that the page loading time improved significantly. Some useful links: