---
lang: en
title: 'API docs: repository.callback'
keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI
sidebar: lb4_sidebar
editurl: https://github.com/strongloop/loopback-next/tree/master/packages/repository
permalink: /doc/en/lb4/apidocs.repository.callback.html
---

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[Home](./index.md) &gt; [@loopback/repository](./repository.md) &gt; [Callback](./repository.callback.md)

## Callback type

Type alias for Node.js callback functions

<b>Signature:</b>

```typescript
export declare type Callback<T> = (err: Error | string | null | undefined, result?: T) => void;
```