function saveUserData(userData) {
  return fetch('/users', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json'
    },
    body: JSON.stringify(userData)
  })
  .then(response => {
    if (response.ok) {
      return Promise.resolve('Data successfully saved');
    } else {
      return Promise.reject('Error saving data');
    }
  })
  .catch(error => {
    return Promise.reject(error.message);
  });
}

// Пример использования
const userData = {
  name: 'John Doe',
  email: '[email protected]',
  age: 30
};

saveUserData(userData)
  .then(message => {
    console.log(message); // Data successfully saved
  })
  .catch(error => {
    console.error(error); // Error saving data
  });