Reduce an array of objects into an object indexed on the specified property.

arrayToObject.js

/**
 * Reduce an array of objects into an object indexed on the specified property.
 *
 * @param  {array}  arr
 * @param  {string} prop
 * @return {object}
 */
function toObject(arr, prop) {
  return arr.reduce((acc, obj) => (
    {...acc, [obj[prop]]: obj}
  ), {});
}

/* Examples
===================================== */

const arrayOfObjects = [
  {id: 'user1', name: 'John'},
  {id: 'user2', name: 'Jane'}
];

toObject(arrayOfObjects, 'id');

/**
 * Output:
 * {
 *   user1: {
 *     id: 'user1',
 *     name: 'John'
 *   },
 *   user2: {
 *     id: 'user2',
 *     name: 'Jane'
 *   }
 * }
 */