44 lines
1.1 KiB
Plaintext
44 lines
1.1 KiB
Plaintext
/**
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* Copyright (c) 2015-present, Facebook, Inc.
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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* @flow strict
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*/
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import type { ObjMap } from './ObjMap';
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/**
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* Creates a keyed JS object from an array, given a function to produce the keys
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* for each value in the array.
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*
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* This provides a convenient lookup for the array items if the key function
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* produces unique results.
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*
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* const phoneBook = [
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* { name: 'Jon', num: '555-1234' },
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* { name: 'Jenny', num: '867-5309' }
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* ]
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*
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* // { Jon: { name: 'Jon', num: '555-1234' },
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* // Jenny: { name: 'Jenny', num: '867-5309' } }
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* const entriesByName = keyMap(
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* phoneBook,
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* entry => entry.name
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* )
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*
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* // { name: 'Jenny', num: '857-6309' }
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* const jennyEntry = entriesByName['Jenny']
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*
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*/
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export default function keyMap<T>(
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list: $ReadOnlyArray<T>,
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keyFn: (item: T) => string,
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): ObjMap<T> {
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return list.reduce(
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(map, item) => ((map[keyFn(item)] = item), map),
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Object.create(null),
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);
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}
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