indexBy.js

const indexBy = (key, xs) => xs.reduce(acc, el) => ({
  ...acc,
  [el[key]]: el,
});

/*
example:
// const users = [
  {id: 'id1', name: 'Aritz'},
  {id: 'id2', name: 'Asier'},
]
const indexedUsers = indexBy('id', users);

{
  id1: {id: 'id1', name: 'Aritz'}
  id2: {id: 'id2', name: 'Asier'}
}
*/