判断一组Radio Button中是否有选中

function alertMessage(f)
            {
                //f = document.Form1
                var flag=false;
                var e = document.all["rbOK"];
                for(var i=0;i<e.length;i++)
                {
                    if(e[i].checked)
                    {
                        flag = true;
                    }
                }
                
                if(flag==false)
                {
                    window.alert("请选择记录!");
                    return false;
                }
                else
                {
                    return true;
                }
            }