Code kata featuring: fetch, promises, array.sort, array.reduce, array.map

kata.js

// 1) fetch members of polish parlament (poslowie)
// 2) group them by occupation
// 3) sort occupations by number of members and occupation name
// 4) get top 5 entries
// 5) print result on the screen
(function() {
    'use strict';

    const POSLOWIE_ENDPOINT = 'https://api-v3.mojepanstwo.pl/dane/poslowie/';

    fetch(POSLOWIE_ENDPOINT)
        .then(response => response.json())
        .then(data => data.Dataobject)
        .then(sumByOccupation)
        .then(occupationsMap => {
            return occupationsMap
                .sort(compareByCountAndName)
                .slice(0, 5);
        })
        .then(printToScreen)
        .catch(e => console.error(e));

     function sumByOccupation(poslowie) {
        return Array.from(
            poslowie
                .map(posel => posel.data['poslowie.zawod'])
                .reduce((map, occupation) => {
                    const numberOfEntries = map.get(occupation) || 0;
                    return map.set(occupation, numberOfEntries + 1);
                }, new Map())
        ).map(([occupation, count]) => {
            return {occupation, count};
        });
     }

     function compareByCountAndName(a, b) {
        return b.count - a.count || (a.occupation).localeCompare(b.occupation); 
     }

     function printToScreen(data) {
        console.table(data);
     }
})();

Sample output: