[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [mapAddToSet](./rc-js-util.mapaddtoset_1.md) ## mapAddToSet() function Used with maps that store sets. Where a set exists for a given key the value will be added to that set, otherwise a new set will be created containing the value. **Signature:** ```typescript export declare function mapAddToSet(map: WeakMap>, key: TKey, value: TValue): void; ``` ## Parameters

Parameter	Type	Description
map	WeakMap<TKey, Set<TValue>>	The `Map` to check. May be modified.
key	TKey	The key to lookup in `map`.
value	TValue	The value to add.

**Returns:** void ## Remarks See [mapAddToSet()](./rc-js-util.mapaddtoset.md).