confirm box in asp.net

Question

function confirm()

{

if (window.confirm("Press a button!") == true) {

return false;

} else {

return false;

}

}

 

 

<asp:Button ID="btnnext" Text="Submit Test" Height="39px" runat="server" OnClientClick="return confirm();" OnClick="btnnext_Click" />

 

 

 i have a error on not available confirm.