Execute javascript function after asp.net postback without Ajax

You should rather use the ScriptManager class, since the Page.ClientScript property is deprecated...

The ClientScriptManager class is new in ASP.NET 2.0 and replaces Page class methods for managing scripts that are now deprecated.
Reference: MSDN - Page.ClientScript Property

The advantage with ScriptManager is that it works with asynchronous postbacks, so if you are using AJAX it will not work with the ClientScriptManager.

Your code would look like this:

ScriptManager.RegisterStartupScript(this, this.GetType(), "ShowPopup", "showCheckOutPopIn('Livraison',556);", true);

Note also that if you are using AJAX and have a piece of javascript code, that you want executed on multiple postbacks, then you should refer to your UpdatePanel in the firstargument e.g.:

ScriptManager.RegisterStartupScript(MainUpdatePanel, typeof(string), "ShowPopup", "showCheckOutPopIn('Livraison',556);", true);

Solution

I needed to add the script tags using the following overload.

Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "script", "alert('Success!');", true);

Found : Re: execute javascript after postback

I don't remember offhand what is the exact syntax/usage for the Page.ClientScript stuff ... that looks like it should work offhand. But if push comes to shove, just have a simple user control that you can enable/disable dynamically that will write out a javascript method in script blocks after the postback. When the page loads, this script execute whatever functionality you wish to execute.

of course, the question is then, what is it that this javascript should do that you couldn't just do on the serverside via some property or other setting that would reflect in the markup?