Check if httponly cookie exists in Javascript

You can indirectly check to see if it exists by trying to set it to a value with javascript if it can't be set, then the HTTP Only Cookie must be there (or the user is blocking cookies).

function doesHttpOnlyCookieExist(cookiename) {
  var d = new Date();
  d.setTime(d.getTime() + (1000));
  var expires = "expires=" + d.toUTCString();

  document.cookie = cookiename + "=new_value;path=/;" + expires;
  return document.cookie.indexOf(cookiename + '=') == -1;
}

Whenever you need to check whether the cookie exists or not, you can send a request to the server that requires authentication & check the response. If its something like 401 Unauthorized or 403 Forbidden, then the cookie probably doesn't exist & you can prompt the user for login.

On the other hand, if the cookie exists, it'll be automatically sent by the browser resulting in a 200 OK response.

I had the same problem. I solved it with the server setting another cookie, not httponly, every time it refreshed the httponly session cookie, with the same max-age and no sensitive data. Now, if one of them is present, the same goes for the other, and the client can know if the httponly counterpart is there.

No. And see Rob's comments below.

See this, which you probably already saw - http://en.wikipedia.org/wiki/HTTP_cookie#Secure_and_HttpOnly

An HttpOnly cookie is not accessible via non-HTTP methods, such as calls via JavaScript (e.g., referencing "document.cookie")...

Edit: Removed undefined response, I wrote a script that you may not be using :)