test.js

const list = [
    { name: 'test a', ranking: 3 },
    { name: 'test b', ranking: 7 },
    { name: 'test c', ranking: 8 },
    { name: 'test d', ranking: 2 },
    { name: 'test e', ranking: 5 },
    { name: 'test f', ranking: 2 },
    { name: 'test g', ranking: 6 },
    { name: 'test h', ranking: 7 },
    { name: 'test i', ranking: 9 },
    { name: 'test j', ranking: 8 },
    { name: 'test k', ranking: 4 },
    { name: 'test l', ranking: 1 },
    { name: 'test m', ranking: 10 },
]

const sortListByRanking = (list) => {
    return list.sort((a, b) => a.ranking - b.ranking);
}

const getAverageRankingFromList = (list) => {
    return list.reduce((a, b) => a + b.ranking, 0) / list.length
}

console.log(sortListByRanking(list));
// expected response
// [ { name: 'test l', ranking: 1 },
//   { name: 'test d', ranking: 2 },
//   { name: 'test f', ranking: 2 },
//   { name: 'test a', ranking: 3 },
//   { name: 'test k', ranking: 4 },
//   { name: 'test e', ranking: 5 },
//   { name: 'test g', ranking: 6 },
//   { name: 'test h', ranking: 7 },
//   { name: 'test b', ranking: 7 },
//   { name: 'test j', ranking: 8 },
//   { name: 'test c', ranking: 8 },
//   { name: 'test i', ranking: 9 },
//   { name: 'test m', ranking: 10 } ]

console.log(getAverageRankingFromList(list));
// expected response
// 5.538461538461538