[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [mapPush](./rc-js-util.mappush_1.md) ## mapPush() function Used with maps that store arrays. Where an array exists for a given key the value will be appended to that array, otherwise a new array will be created containing the value. **Signature:** ```typescript export declare function mapPush(map: WeakMap, key: TKey, value: TValue): void; ``` ## Parameters

Parameter	Type	Description
map	WeakMap<TKey, TValue\[\]>	The `Map` to check. May be modified.
key	TKey	The key to lookup in `map`.
value	TValue	The value to push.

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