[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [mapUnion](./rc-js-util.mapunion.md) ## mapUnion() function Returns a map with keys from both A and B. If both A and B have the same key the value from B will be used. **Signature:** ```typescript export declare function mapUnion(a: ReadonlyMap, b: ReadonlyMap): Map; ``` ## Parameters

Parameter	Type	Description
a	ReadonlyMap<TKey, TIem>
b	ReadonlyMap<TKey, TIem>

**Returns:** Map<TKey, TIem> ## Remarks See [mapUnion()](./rc-js-util.mapunion.md).