var cities = [
    {country: "Indonesia", city: "Jakarta", population: 30539},
    {country: "France",    city: "Paris",   population: 10858},
    {country: "Egypt",     city: "Cairo",   population: 25600},
    {country: "Japan",     city: "Tokyo",   population: 37843},
    {country: "Russia",    city: "Moscow",  population: 16170}
];
 
function max(cities, n) {
    var citiesCopy = cities.slice();
    citiesCopy.sort(function(a, b) {
        return (a.population < b.population) ? 1 : -1;
    });
    citiesCopy = citiesCopy.map(function(item) {
        return item.city;
    });
    return citiesCopy.slice(0, n);
}
console.log(max(cities, 3));
 

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