/**
 *  Copyright (c) 2015, Facebook, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant
 *  of patent rights can be found in the PATENTS file in the same directory.
 */ /**
 * Creates a keyed JS object from an array, given a function to produce the keys
 * for each value in the array.
 *
 * This provides a convenient lookup for the array items if the key function
 * produces unique results.
 *
 *     const phoneBook = [
 *       { name: 'Jon', num: '555-1234' },
 *       { name: 'Jenny', num: '867-5309' }
 *     ]
 *
 *     // { Jon: { name: 'Jon', num: '555-1234' },
 *     //   Jenny: { name: 'Jenny', num: '867-5309' } }
 *     const entriesByName = keyMap(
 *       phoneBook,
 *       entry => entry.name
 *     )
 *
 *     // { name: 'Jenny', num: '857-6309' }
 *     const jennyEntry = entriesByName['Jenny']
 *
 */ export default function keyMap < T > ( list , keyFn ) { return list . reduce ( ( map , item ) => ( ( map [ keyFn ( item ) ] = item ) , map ) , { } ) ; }