## flatMapFilter() function [​](/content/docs/sdk/core.flatmapfilter#flatmapfilter-function/index.html)

**Signature:**

```typescript
export declare function flatMapFilter<T, U>(arr: T[] | undefined, fn: (value: T, idx: number) => U | U[] | undefined): U[];
```

## Parameters [​](/content/docs/sdk/core.flatmapfilter#parameters/index.html)

| Parameter | Type | Description |
| --- | --- | --- |
| arr | T[] | | undefined |  |
| fn | (value: T, idx: number) => U | U[] | undefined |  |

**Returns:**

U[]

- [flatMapFilter() function](/content/docs/sdk/core.flatmapfilter#flatmapfilter-function/index.html)
- [Parameters](/content/docs/sdk/core.flatmapfilter#parameters/index.html)