var shanhai = { name: "Шанхай", population: 23416 };
var jakarta = { name: "Джакарта", population: 30539 };
var pekin = { name: "Пекин", population: 21009 };
var deli = { name: "Дели", population: 24998 };
var manila = { name: "Манила", population: 24123 };
 
var cities = [shanhai, jakarta, pekin, deli, manila];
 
function sort(city1, city2) {
	return city2.population - city1.population;		//Заменим местами 1 и 2 и получим уже по возрастанию.
}
 
function populationSort(arr, x) {
	var newArr = arr.sort(sort);
	newArr = newArr.slice(0, x);
	var newNewArr = [];					//newNewArr :)
 
		for (var i = 0; i < x; i++) {
			newNewArr[i] = newArr[i].name; 
		};
		return newNewArr;
}
 
console.log(populationSort(cities, 5));

dmFyIHNoYW5oYWkgPSB7IG5hbWU6ICLQqNCw0L3RhdCw0LkiLCBwb3B1bGF0aW9uOiAyMzQxNiB9Owp2YXIgamFrYXJ0YSA9IHsgbmFtZTogItCU0LbQsNC60LDRgNGC0LAiLCBwb3B1bGF0aW9uOiAzMDUzOSB9Owp2YXIgcGVraW4gPSB7IG5hbWU6ICLQn9C10LrQuNC9IiwgcG9wdWxhdGlvbjogMjEwMDkgfTsKdmFyIGRlbGkgPSB7IG5hbWU6ICLQlNC10LvQuCIsIHBvcHVsYXRpb246IDI0OTk4IH07CnZhciBtYW5pbGEgPSB7IG5hbWU6ICLQnNCw0L3QuNC70LAiLCBwb3B1bGF0aW9uOiAyNDEyMyB9OwoKdmFyIGNpdGllcyA9IFtzaGFuaGFpLCBqYWthcnRhLCBwZWtpbiwgZGVsaSwgbWFuaWxhXTsKCmZ1bmN0aW9uIHNvcnQoY2l0eTEsIGNpdHkyKSB7CglyZXR1cm4gY2l0eTIucG9wdWxhdGlvbiAtIGNpdHkxLnBvcHVsYXRpb247CQkvL9CX0LDQvNC10L3QuNC8INC80LXRgdGC0LDQvNC4IDEg0LggMiDQuCDQv9C+0LvRg9GH0LjQvCDRg9C20LUg0L/QviDQstC+0LfRgNCw0YHRgtCw0L3QuNGOLgp9CgpmdW5jdGlvbiBwb3B1bGF0aW9uU29ydChhcnIsIHgpIHsKCXZhciBuZXdBcnIgPSBhcnIuc29ydChzb3J0KTsKCW5ld0FyciA9IG5ld0Fyci5zbGljZSgwLCB4KTsKCXZhciBuZXdOZXdBcnIgPSBbXTsJCQkJCS8vbmV3TmV3QXJyIDopCgoJCWZvciAodmFyIGkgPSAwOyBpIDwgeDsgaSsrKSB7CgkJCW5ld05ld0FycltpXSA9IG5ld0FycltpXS5uYW1lOyAKCQl9OwoJCXJldHVybiBuZXdOZXdBcnI7Cn0KCmNvbnNvbGUubG9nKHBvcHVsYXRpb25Tb3J0KGNpdGllcywgNSkpOw==