function setCookie(){
var scroll=typeof window.pageYOffset != 'undefined' ? window.pageYOffset 
: document.documentElement.scrollTop;
document.cookie='yscroll' + "=" + scroll;
}
window.onscroll=setCookie;


function delete_cookie ( cookie_name )
{
  var cookie_date = new Date ( );  // current date & time
  cookie_date.setTime ( cookie_date.getTime() - 1 );
  document.cookie = cookie_name += "=; expires=" + 
cookie_date.toGMTString();
}