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

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[Home](./index.md) &gt; [@loopback/express](./express.md) &gt; [MiddlewareOrKey](./express.middlewareorkey.md)

## MiddlewareOrKey type

A middleware function or binding key

**Signature:**

```typescript
export type MiddlewareOrKey = GenericInterceptorOrKey<MiddlewareContext>;
```
**References:** [GenericInterceptorOrKey](./context.genericinterceptororkey.md)<!-- -->, [MiddlewareContext](./express.middlewarecontext.md)