function setCookie(c_name,value,expiredays)
{
var exdate=new Date()
exdate.setDate(exdate.getDate()+expiredays)
document.cookie=c_name+ "=" +escape(value)+
((expiredays==null) ? "" : ";expires="+exdate.toGMTString())
}

//取回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 ""
}

setCookie('username','123',365);

getCookie('username');