How to optimize Cookie Parsing?
Like I wrote in my comment, the function you've got isn't really a parser. Yes, it parses the strings you pass it, but that's not its purpose, as far as I can tell. Parsing is a byproduct of the actual purpose, which seems to be to sanitize the strings by removing the domain key/value pair.

Now, if you're just looking to remove that key/value pair, you could simply do

function sanitizeCookies(strings) {
  return strings.map(function (cookieString) {
     return cookieString.replace(/\bdomain\s*=[^;]*;?/ig, "");
  });
}


Like @tomdemuyt, I'm using Array.map() so you won't get null back if you pass it an empty array; you'll just get another empty array (and, frankly, that makes more sense, I think).