interface User {
  _id: string;
  name: string;
}

function stringFilter(q: unknown): Filter<User> {
  const query: Filter<User> = {};
  if (q && typeof q === "string") {
    query.$text = {
      $search: q,
      $caseSensitive: false,
      $diacriticSensitive: false,
      $language: "en",
    };
  }
  return query;
}

const query = stringFilter("search");
let results = collection.find(query);