Group an array of object by a specified key

groupBy.js

/**
 * Group an array of object by a specified key
 * @param {array} items Array of objects
 * @param {string} key Key to use for grouping
 * @returns {object}
 */
const groupBy = (items, key) => {
  return items.reduce(
    (result, item) => ({
      ...result,
      [item[key]]: [...(result[item[key]] || []), item],
    }),
    {}
  )
}