Maps array of objets to a key value object using key provided

mapKeys.js

const mapKeys = (collection, rootKey) => {
  const obj = {};
  collection.forEach(item => {
    obj[item[rootKey]] = item;
  });
  return obj;
};

const justins = [{id: 1, name: 'Justin Bieber'},{id: 2, name: 'Justin Timberlake'},{id: 3, name: 'Justin Time'}];

mapKeys(justins, 'id');

// {
//  1: {id: 1, name: 'Justin Bieber'},
//  2: {id: 2, name: 'Justin Timberlake'},
//  3: {id: 3, name: 'Justin Time'}
//}