JS判断父窗体中的函数是否存在

function returnopen(retbutton,retnamebutton,retvalue,retnamevalue)
        {
                window.opener.document.all(retbutton,0).value=retvalue;
                window.opener.document.all(retnamebutton,0).value=retnamevalue;
                window.opener.document.all(retnamebutton,0).focus();
                window.close();
                
                if (typeof(window.opener.ReRender)!="undefined"){
                    window.opener.ReRender();
                }    //添加者：Herist；用以回调刷新select控件                
        }