actions must be plain objects. use custom middleware for async actions.

fetch(`https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${apiKey}`)
  .then(response => response.json())
  .then(weather => {
    console.log(weather);
    return {
      type: CITY_WEATHER,
      payload: weather
    }
  });
}

fetch(`https://api.openweathermap.org/data/2.5/weather?q=${city}&appid=${apiKey}`)
  .then(response => response.json())
  .then(weather => {
    console.log(weather);
    return {
      type: CITY_WEATHER,
      payload: weather
    }
  });
}