js 读取和清除cookie

function getCookie(c_name){
   if(document.cookie.length>0){
     c_start=document.cookie.indexOf(c_name + "=");
     if (c_start!=-1){
      c_start=c_start + c_name.length+1;
      c_end=document.cookie.indexOf(";",c_start);
     if(c_end==-1)
      c_end=document.cookie.length;
     return unescape(document.cookie.substring(c_start,c_end));
     }
   }
   return ""
  }
  
  function clearCookie(c_name){
   var value="";
   var Days = 30;
   var exp  = new Date();    //new Date("December 31, 9998");
      exp.setTime(exp.getTime() + Days*24*60*60*1000);
   document.cookie=c_name+ "=" +escape(value) + ";expires=" + exp.toGMTString();
  }