Nuxt/docs/6.bridge/4.plugins-and-middleware.md

# Plugins and Middleware

## New Plugins Format

You can now migrate to the Nuxt 3 plugins API, which is slightly different in format from Nuxt 2.

Plugins now take only one argument (`nuxtApp`). You can find out more in [the docs](/docs/guide/directory-structure/plugins).

```js
export default defineNuxtPlugin(nuxtApp => {
  nuxtApp.provide('injected', () => 'my injected function')
  // now available on `nuxtApp.$injected`
})
```

::alert
If you want to use the new Nuxt composables (such as [`useNuxtApp`](/docs/api/composables/use-nuxt-app) or `useRuntimeConfig`) within your plugins, you will need to use the `defineNuxtPlugin` helper for those plugins.
::

::alert{type=warning}
Although a compatibility interface is provided via `nuxtApp.vueApp` you should avoid registering plugins, directives, mixins or components this way without adding your own logic to ensure they are not installed more than once, or this may cause a memory leak.
::

## New Middleware Format

You can now migrate to the Nuxt 3 middleware API, which is slightly different in format from Nuxt 2.

Middleware now take only two argument (`to`, `from`). You can find out more in [the docs](/docs/guide/directory-structure/middleware).

```js
export default defineNuxtRouteMiddleware((to) => {
  if (to.path !== '/') {
    return navigateTo('/')
  }
})
```

::alert{type=warning}
Use of `defineNuxtRouteMiddleware` is not supported outside of the middleware directory.
::

::alert{type=warning}
Nuxt Bridge does not support `definePageMeta`.
::