ASP.NET web page goes blank with JavaScript alert()

Here is a simpler version. Using the overload method[^](parameter addScriptTags), you can reduce the code.

private void ShowMessage(string Message)
{
  if (!ClientScript.IsClientScriptBlockRegistered("MyMessage"))
  {
    ClientScript.RegisterClientScriptBlock(this.GetType(), "MyMessage", "alert('" + Message + "');", true);
  }
}
 
public void btnTest_Click(Object sender, EventArgs e)
{
  ShowMessage("Hello World");
}

For AJAX - Updatepanel, use the below one:

ScriptManager.RegisterClientScriptBlock(this.Page, typeof(UpdatePanel), "MyMessage", Message, true);

 
EDIT
The alert keyword moved into general function ShowMessage.

Further Reading

• ClientScriptManager.RegisterClientScriptBlock Method[^]
• ScriptManager.RegisterClientScriptBlock Method[^]