How to modify this code to close Page without Y/N Prompt ?

I am using the following code to close the existing page but the user's browers come up with a prompt asking Yes No. I want it close without any prompt. Is there way to add parameter to skip the Y/N prompt ?
Thanks !! 
 
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
  
  
  
       <script type="text/javascript">
   
       //Closes the browser window
       function CloseWindow()
       {
          window.opener = 'x';
          window.close();
       }
      ...