[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [arrayIndex](./rc-js-util.arrayindex.md) ## arrayIndex() function Populates a `Map` given a key creating function and `ArrayLike`. **Signature:** ```typescript export declare function arrayIndex(items: ArrayLike, getKey: (item: TItem, index: number) => TKey | null): Map, TItem>; ``` ## Parameters

Parameter	Type	Description
items	ArrayLike<TItem>
getKey	(item: TItem, index: number) => TKey \| null

**Returns:** Map<Exclude<TKey, null>, TItem> ## Remarks keys which are null are omitted. See [arrayIndex()](./rc-js-util.arrayindex.md).