rc-js-util/src/array/impl/array-index.ts

A collection of TS and C++ utilities to help writing performant and correct applications, achieved through strict typing and (removable) invariant checking.

/**
 * @public
 * Populates a `Map` given a key creating function and `ArrayLike`.
 *
 * @remarks
 * keys which are null are omitted.
 *
 * See {@link arrayIndex}.
 */
export function arrayIndex<TKey, TItem>
(
    items: ArrayLike<TItem>,
    getKey: (item: TItem, index: number) => TKey | null
)
    : Map<Exclude<TKey, null>, TItem>
{
    const indexed = new Map<Exclude<TKey, null>, TItem>();

    for (let i = 0, iEnd = items.length; i < iEnd; ++i)
    {
        const item = items[i];
        const key = getKey(item, i);

        if (key !== null)
        {
            indexed.set(key as Exclude<TKey, null>, item);
        }
    }

    return indexed;
}