current-temperatures.js

// An object that will contain the current temperatures of the cities
// The keys are the city names, while the values are their current temperatures (in °C)
let TEMPS = null;

// The maximum number of retries for failed temperature fetches
const MAX_TEMP_FETCH_RETRIES = 5;

/**
 * Fetches the current temperatures of multiple cities (in °C) and update the `TEMPS` object.
 * Also schedule retries for failed temperature fetches.
 * @param {Array} cities The cities to fetch their current temperatures
 * @param {number} retries The current number of retries so far
 * @returns {Promise} A promise that is fulfilled with the updated `TEMPS` object.
 */
const fetchTemperatures = (cities, retries = 0) => {
  return fetchTempForCities(cities)
    .then(temps => {
    
      // Update the `TEMPS` object with updated city temperatures from `temps`
      TEMPS = (TEMPS === null) ? temps : { ...TEMPS, ...temps };
    
      // Filter the keys (cities) of the `TEMPS` object to get a list of the cities
      // with `null` temperature values.
      const RETRY_CITIES = Object.keys(TEMPS)
        .filter(city => TEMPS[city] == null);

      // If there are 1 or more cities in the `RETRY_CITIES` list
      // and the maximum retries has not been exceeded,
      // attempt to fetch their temperatures again after waiting for 5 seconds.
      // Also increment `retries` by 1.
    
      if (RETRY_CITIES.length > 0 && retries < MAX_TEMP_FETCH_RETRIES) {
        setTimeout(() => fetchTemperatures(RETRY_CITIES, ++retries), 5 * 1000);
      }
    
      // Return the updated `TEMPS` object
      return TEMPS;
    
    })
    .then(console.log, console.error);
}

// Fetch the current temperatures of the cities in the `CITIES` list
// and update the `TEMPS` object
fetchTemperatures(CITIES);