使用CookieHelper幫助類：

public class CookieHelper
    {

        #region 獲取Cookie


        /// <summary> 
        /// 獲得Cookie的值 
        /// </summary> 
        /// <param name="cookieName"></param> 
        /// <returns></returns> 
        public static string GetCookieValue(string
 
 cookieName)
        {
            HttpRequest request = HttpContext.Current.Request;
            if (request != null)
                return GetCookieValue(request.Cookies[cookieName]);
            return "";
        }

        /// <summary> 
        /// 獲得Cookie的值 
        /// </summary> 
        ///
 
 <param name="cookie"></param> 
        /// <returns></returns> 
        public static string GetCookieValue(HttpCookie cookie)
        {
            if (cookie != null)
            {
                return cookie.Value;
            }
            return "";
        }

        /// <summary>
 
 
        /// 獲得Cookie 
        /// </summary> 
        /// <param name="cookieName"></param> 
        /// <returns></returns> 
        public static HttpCookie GetCookie(string cookieName)
        {
            HttpRequest request = HttpContext.Current.Request;
            if (request != null)
                return request.Cookies[cookieName];
            return null;
        }

        #endregion

        #region 刪除Cookie


        /// <summary> 
        /// 刪除Cookie
        /// </summary> 
        /// <param name="cookieName"></param> 
        public static void RemoveCookie(string cookieName)
        {
            HttpResponse response = HttpContext.Current.Response;
            if (response != null)
            {
                HttpCookie cookie = response.Cookies[cookieName];
                if (cookie != null)
                {
                     response.Cookies.Remove(cookieName);
                }
            }
        }

        #endregion

        #region 設定/修改Cookie
         

        /// <summary> 
        /// 設定Cookie 
        /// </summary> 
        /// <param name="cookieName"></param> 
        /// <param name="key"></param> 
        /// <param name="value"></param> 
        /// <param name="expires"></param> 
        public static void SetCookie(string cookieName,string value, DateTime? expires)
        {
            Guard.IsNotNullOrEmpty(cookieName, "cookieName"); 

            HttpResponse response = HttpContext.Current.Response;
            if (response != null)
            {
                HttpCookie cookie = response.Cookies[cookieName];
                if (cookie != null)
                {
                    cookie.Value = value; 
                    if (expires != null)
                        cookie.Expires = expires.Value;
                    response.SetCookie(cookie);
                }
            }

        }

        #endregion

        #region 新增Cookie
         
         

        /// <summary> 
        /// 新增為Cookie.Values集合 
        /// </summary> 
        /// <param name="cookieName"></param> 
        /// <param name="key"></param> 
        /// <param name="value"></param> 
        /// <param name="expires"></param> 
        public static void AddCookie(string cookieName,  string value, DateTime expires)
        {
            Guard.IsNotNullOrEmpty(cookieName, "cookieName");

            HttpCookie cookie = new HttpCookie(cookieName);
            cookie.Expires = expires;
            cookie.Value = value;
            AddCookie(cookie);
        }

        /// <summary> 
        /// 新增Cookie 
        /// </summary> 
        /// <param name="cookie"></param> 
        public static void AddCookie(HttpCookie cookie)
        {
            HttpResponse response = HttpContext.Current.Response;
            if (response != null)
            {
                //指定客戶端指令碼是否可以訪問[預設為false] 
                cookie.HttpOnly = true;
                //指定統一的Path，比便能通存通取 
                cookie.Path = "/";
                //設定跨域,這樣在其它二級域名下就都可以訪問到了 
                //cookie.Domain = "nas.com"; 
                response.AppendCookie(cookie);
            }
        }

        #endregion
    }

設定cookie：

   public static string VCLoginName
        {
            get
            {
                try
                {
                    return CookieHelper.GetCookieValue("VCLoginName").ToStr();
                }
                catch
                {
                    return "0";
                }
            }
            set
            {
                var cookie = CookieHelper.GetCookie("VCLoginName");
                if (cookie != null)
                {
                    CookieHelper.SetCookie("VCLoginName", value, DateTime.Now.AddHours(1));
                }
                else
                {
                    //有效期，一個鐘頭
                    CookieHelper.AddCookie("VCLoginName", value, DateTime.Now.AddHours(1));
                }

            }
        }

設定：

 SysContext.VCLoginName = user.LoginName;

js獲取和設定cookie：

 function getCookie(cname) {
            console.log("開始")
            console.log(document.cookie)
            console.log("結束")
            var arrStr = document.cookie.split("; ");
           
            for (var i = 0; i < arrStr.length; i++) {

                var temp = arrStr[i].split("=");

                if (temp[0] == cname) return unescape(temp[1]);

            }

        }

 //新增cookie
        function addCookie(cname, cvalue, ctime) {
            var str = cname + "=" + escape(cvalue);
            if (ctime > 0) {                               //為時不設定過期時間，瀏覽器關閉時cookie自動消失
                var date = new Date();
                var ms = ctime * 3600 * 1000;
                date.setTime(date.getTime() + ms);
                str += "; expires=" + date.toGMTString();
                alert(cname + cvalue);
            }
            document.cookie = str;
        }

遇到的問題:

後臺設定cookie但是通過js無法獲取相應的cookie的值，why？

不知道。但是自己在一般處理程式中寫的cookie卻可以通過js獲得。why？

 HttpCookie cookie = new HttpCookie("LoginName", HttpUtility.UrlEncode(username)); //定義cookie物件以及名為DocUrl的項 
        DateTime dt = DateTime.Now;                  //定義時間物件 
        TimeSpan ts = new TimeSpan(0, 12, 20, 0);         //天，小時，分鐘，秒  ,cookie有效作用時間
        cookie.Expires = dt.Add(ts);                 //新增作用時間 
        context.Response.AppendCookie(cookie);               //確定寫入cookie中

解決：

因為CookieHelper中設定了cookie的HttpOnly為true。

ASP.Net中HttpCookie物件的HttpOnly 屬性 指定一個Cookie 是否可通過客戶端指令碼訪問。不能通過客戶端指令碼訪問為 true；否則為 false。預設值為 false。此屬性並不能完全阻止客戶端在本地獲取cookies，但是可以增加通過指令碼直接獲取的難度。