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// @flow strict
import type { ObjMap } from './ObjMap';
/**
* 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: $ReadOnlyArray<T>,
keyFn: (item: T) => string,
): ObjMap<T> {
return list.reduce((map, item) => {
map[keyFn(item)] = item;
return map;
}, Object.create(null));
}
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