keyValMap.mjs

/**
 * Creates a keyed JS object from an array, given a function to produce the keys
 * and a function to produce the values from each item in the array.
 *
 *     const phoneBook = [
 *       { name: 'Jon', num: '555-1234' },
 *       { name: 'Jenny', num: '867-5309' }
 *     ]
 *
 *     // { Jon: '555-1234', Jenny: '867-5309' }
 *     const phonesByName = keyValMap(
 *       phoneBook,
 *       entry => entry.name,
 *       entry => entry.num
 *     )
 *
 */
export default function keyValMap(list, keyFn, valFn) {
  return list.reduce(function (map, item) {
    map[keyFn(item)] = valFn(item);
    return map;
  }, Object.create(null));
}