怎么在html中，用js判断session是否存在

  function checsessoin()
   {
      var strSession = "<%=Session["uid"] %>".toString(); 
       if( strSession == "")
       {
          alert('请先登录');
          return false;
        }
    }

一般的, session 是通过 cookie 来维持的, cookie 的名字可以通过配置指定一个名称
mode="[Off|InProc|StateServer|SQLServer|Custom]"
timeout="number of minutes"
cookieName="session identifier cookie name"
cookieless=
"[true|false|AutoDetect|UseCookies|UseUri|UseDeviceProfile]"
regenerateExpiredSessionId="[True|False]"
sqlConnectionString="sql connection string"
sqlCommandTimeout="number of seconds"
allowCustomSqlDatabase="[True|False]"
useHostingIdentity="[True|False]"
stateConnectionString="tcpip=server:port"
stateNetworkTimeout="number of seconds"
customProvider="custom provider name">
...

在 js 中可以判断这个名称的 cookie 是否存在.
function getCookie(name) {
var cookies = document.cookie.split(";");
for (var i = 0; i < cookies.length; ++i) {
var a = cookies[i].split("=");
if (a.length == 2) {
a[0] = a[0].trim();
a[1] = a[1].trim();
if (a[0] == name) {
return unescape(a[1]);
}
}
}
return "";
}