veritatisdoloremque/docs-exp/auth-types.nextorobserver.md

Monorepo for the Firebase JavaScript SDK

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[Home](./index.md) &gt; [@firebase/auth-types](./auth-types.md) &gt; [NextOrObserver](./auth-types.nextorobserver.md)

## NextOrObserver type

Type definition for an event callback.

<b>Signature:</b>

```typescript
export type NextOrObserver<T> = NextFn<T | null> | Observer<T | null>;
```