City Sort

citySort.js

const cities = [
  { "San Francisco": 3000 },
  { "Los Angeles": 5000 },
  { "San Francisco": 3000 },
  { Sacramento: 2000 }
];

const uniqueCityFilter = (cityObject, index, array) => {
  return (
    index ===
    array.findIndex(s => {
      const cityName = Object.keys(s)[0];
      const currentCityName = Object.keys(cityObject)[0];
      return cityName === currentCityName;
    })
  );
};

const sumCityPopulation = (population, currentCity, cityArray) => {
  const cityPopulation = Object.values(currentCity)[0];
  return population + cityPopulation;
};

const total = cities.filter(uniqueCityFilter).reduce(sumCityPopulation, 0);

console.log(total);