type MapOptions<T, U = T> = {
    /**
     * Allow merging existing keys or not, if not keys will be overriden if they exist
     * (default=false)
     *
     * Example:
     *  mapKey([{uid: 12, a: 'hi'}, {uid: 12, b: 'ho'}], 'uid', {merge: true})
     * Output:
     *  {12: {uid: 12, a: 'hi', b: 'ho'}}
     * Output if merge is false
     *  {12: {uid: 12, b: 'ho'}}
     */
    merge?: boolean;
    /**
     * Pass a custom filter function which will be run in O(n) while iterating
     */
    filter_fn?: (el: T) => boolean;
    /**
     * A custom transformer function to modify each element before mapping.
     * Its output type `U` becomes the value type of the resulting map.
     */
    transform_fn?: (el: T) => U;
};
/**
 * Map an object array into a Map by passing a common key that exists on the objects. Objects for
 * which the key doesn't exist will be filtered out automatically
 *
 * Example:
 *  mapKey([{uid: 12, name: 'Peter'}, {uid: 15, name: 'Jonas'}], 'uid');
 * Output:
 *  new Map([
 *    [12, {uid: 12, name: 'Peter'}],
 *    [15, {uid: 15, name: 'Jonas'}],
 *  ])
 *
 * @param {Record<string,any>[]} val - Array to map
 * @param {string} key - Key to map by
 * @param {MapOptions?} opts - Options object to override built-in defaults
 */
declare function mapKeyAsMap<T extends Record<string, any>, U extends Record<string, any> = T, TKey extends keyof T = string>(arr: T[], key: TKey, opts?: MapOptions<T, U>): Map<T[TKey], U>;
export { mapKeyAsMap, mapKeyAsMap as default };