text: class Db {
      constructor() {
          this.users = {};
      }
      find(username) {
          console.log(`db find ${username}`);
          if(this.users[username]) {
              return {username, password: this.users[username]};
          } else {
              console.log(`[DB] no user: ${username}`);
  
              return;
          }
      }
      save(username, password) {
          console.log(`db save ${username} ${password}`);
          if (this.users[username]) {
              console.log(`${username} exists: ${this.users[username]}`);
          }
          this.users[username] = password;
      }
  };
  
  module.exports = new Db();