h3/dist/docs/0.guide/1.basics/6.nested-apps.md

Minimal H(TTP) framework built for high performance and portability.

# Nested Apps

> H3 has a native `mount` method for adding nested sub-apps to the main instance.

Typically, H3 projects consist of several [Event Handlers](/guide/basics/handler) defined in one or multiple files (or even [lazy loaded](/guide/basics/handler#lazy-handlers) for faster startup times).

It is sometimes more convenient to combine multiple `H3` instances or even use another HTTP framework used by a different team and mount it to the main app instance. H3 provides a native [`.mount`](/guide/api/h3#h3mount) method to facilitate this.

## Nested H3 Apps

H3 natively allows mounting sub-apps. When mounted, sub-app routes and middleware are **merged** with the base url prefix into the main app instance.

```js
import { H3, serve } from "h3";

const nestedApp = new H3()
  .use((event) => {
    event.res.headers.set("x-api", "1");
  })
  .get("/**:slug", (event) => ({
    pathname: event.url.pathname,
    slug: event.context.params?.slug,
  }));

const app = new H3().mount("/api", nestedApp);
```

In the example above, when fetching the `/api/test` URL, `pathname` will be `/api/test` (the real path), and `slug` will be `/test` (wildcard param).

> [!NOTE]
> Global config and hooks won't be inherited from the nested app. Consider always setting them from the main app.

## Nested Web Standard Apps

Mount a `.fetch` compatible server instance like [Hono](https://hono.dev/) or [Elysia](https://elysiajs.com/) under the base URL.

> [!NOTE]
> Base prefix will be removed from `request.url` passed to the mounted app.

```js
import { H3 } from "h3";
import { Hono } from "hono";
import { Elysia } from "elysia";

const app = new H3()
  .mount(
    "/elysia",
    new Elysia().get("/test", () => "Hello Elysia!"),
  )
  .mount(
    "/hono",
    new Hono().get("/test", (c) => c.text("Hello Hono!")),
  );
```

> [!TIP]
> Similarly, you can mount an H3 app in [Hono](https://hono.dev/docs/api/hono#mount) or [Elysia](https://elysiajs.com/patterns/mount#mount-1).