nta2-1.js

import _ from 'lodash';

export const indexBooksByAuthor = (books) => {
  return _.reduce(books, (acc, e) => {
    acc[e.authorId] = e
    return acc
  }, {});
}

export const getSomeValue = () => {
  // some code ...

  const booksByAuthor = indexBooksByAuthor(books);

  // some more code ...
}