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

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[Home](./index.md) &gt; [@loopback/rest](./rest.md) &gt; [RestApplication](./rest.restapplication.md) &gt; [handler](./rest.restapplication.handler.md)

## RestApplication.handler() method

**Signature:**

```typescript
handler(handlerFn: SequenceFunction): void;
```

## Parameters

|  Parameter | Type | Description |
|  --- | --- | --- |
|  handlerFn | [SequenceFunction](./rest.sequencefunction.md) |  |

**Returns:**

void