Cookies con Javascript

Come si gestiscono i cookie con JavaScript? Quirkmodes presenta questo frammento di codice molto utile e pulito:

function createCookie(name, value, days) 
{
 if (days) 
 {
  var date = new Date();
  date.setTime(date.getTime()+(days*24*60*60*1000));
  var expires = "; expires="+date.toGMTString();
 }
 else 
 {
   var expires = "";
 }
 document.cookie = name+"="+value+expires+"; path=/";
}

function readCookie(name) 
{
 var nameEQ = name + "=";
 var ca = document.cookie.split(';');
 for(var i=0;i < ca.length;i++) {
  var c = ca[i];
  while (c.charAt(0)==' ') c = c.substring(1,c.length);
  if (c.indexOf(nameEQ) == 0) return c.substring(nameEQ.length,c.length);
 }
 return null;
}

function eraseCookie(name) 
{
  createCookie(name,"",-1);
}