javascriptはcookieを植えて、cookieを読みます.

var exdate=new Date();
exdate.setDate(exdate.getDate()+1);
document.cookie="manu_username"+ "=" +escape(username)+";expires="+exdate.toGMTString()+";path=/";

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 "";
}