返回上一頁，返回到最後一頁的時候回調

 function goBack(){
        if ((navigator.userAgent.indexOf('MSIE') >= 0) && (navigator.userAgent.indexOf('Opera') < 0)){ // IE
            if(history.length > 0){
                window.history.go( -1 );
            }else{
                window.opener=null;window.close();
            }
        }else{ //非IE瀏覽器
            if (navigator.userAgent.indexOf('Firefox') >= 0 ||
                    navigator.userAgent.indexOf('Opera') >= 0 ||
                    navigator.userAgent.indexOf('Safari') >= 0 ||
                    navigator.userAgent.indexOf('Chrome') >= 0 ||
                    navigator.userAgent.indexOf('WebKit') >= 0){

                if(window.history.length > 1){
                    window.history.go( -1 );
                }else{
                    window.opener=null;window.close();
                }
            }else{ //未知的瀏覽器
                window.history.go( -1 );
            }
        }
    }