js弹出窗体获得焦点

function openwindow( )
{
  window.status="系统当前状态：您正在注册用户......";
  if (window.screen.width == 1024 && window.screen.height == 768)
    window.showModalDialog("register.html", "注册窗口", "toolbars=0, location=0, statusbars=0, menubars=0,width=700,height=550,scrollbars=1");
  else
    window.alert("请设置分辨率为1024x768，然后再打开");

}
function closewindow( )
{
  if(window.confirm("您确认要退出系统吗？"))
    window.close( );
}