cookie添加删除修改

   //cookie添加
            document.cookie="username=John Doe";
            //添加过期时间
            document.cookie="username1=John Doe1; expires=Thu, 18 Dec 2013 12:00:00 GMT";
           //用 path 参数告诉浏览器 cookie 的路径。默认情况下，cookie 属于当前页面。
            document.cookie="username2=John Doe2; expires=Thu, 18 Dec 2013 12:00:00 GMT; path=/";
            //读取 Cookie
            var x = document.cookie;
            console.log(x);
            //修改 Cookie  也是创建新的覆盖旧的

           //删除 Cookie  把期限设置成以前的时间
           document.cookie = "username=; expires=Thu, 01 Jan 1970 00:00:00 GMT";

           //设置 cookie 值的函数   该函数设置了 cookie 名、cookie 值、cookie过期时间。
           function setCookie(cname,cvalue,exdays)
            {
              var d = new Date();
              d.setTime(d.getTime()+(exdays*24*60*60*1000));
              var expires = "expires="+d.toGMTString();
              document.cookie = cname + "=" + cvalue + "; " + expires;
            }

            //获取 cookie 值的函数
            function getCookie(cname)
            {
              var name = cname + "=";
              var ca = document.cookie.split(';');
              for(var i=0; i<ca.length; i++) 
              {
                var c = ca[i].trim();
                if (c.indexOf(name)==0) return c.substring(name.length,c.length);
              }
              return "";
            }


            //检测 cookie 值的函数
            function checkCookie()
            {
              var username=getCookie("username");
              if (username!="")
              {
                alert("Welcome again " + username);
              }
              else 
              {
                username = prompt("Please enter your name:","");
                if (username!="" && username!=null)
                {
                  setCookie("username",username,365);
                }
              }
            }