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lang: en
title: 'API docs: rest.restserver.mountexpressrouter'
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.restserver.mountexpressrouter.html
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[Home](./index.md) > [@loopback/rest](./rest.md) > [RestServer](./rest.restserver.md) > [mountExpressRouter](./rest.restserver.mountexpressrouter.md)
## RestServer.mountExpressRouter() method
Mount an Express router to expose additional REST endpoints handled via legacy Express-based stack.
<b>Signature:</b>
```typescript
mountExpressRouter(basePath: string, router: ExpressRequestHandler, spec?: RouterSpec): void;
```
## Parameters
| Parameter | Type | Description |
| --- | --- | --- |
| basePath | string | Path where to mount the router at, e.g. <code>/</code> or <code>/api</code>. |
| router | [ExpressRequestHandler](./express.expressrequesthandler.md) | The Express router to handle the requests. |
| spec | [RouterSpec](./rest.routerspec.md) | A partial OpenAPI spec describing endpoints provided by the router. LoopBack will prepend <code>basePath</code> to all endpoints automatically. This argument is optional. You can leave it out if you don't want to document the routes. |
<b>Returns:</b>
void