//读取cookie

function readCookie(name){
var nameEQ=name+"=";
var ca=document.cookie.split(';');
for(var i=0;i<ca.length;i++){
   var c=ca[i];var idx=0;
while(c.charAt(idx)==' ')idx++;
if(idx>0)c=c.substr(idx);
if(c.indexOf(nameEQ)==0)return c.substr(nameEQ.length);
 }
return null;
  }