# Source: https://nuxt.com/raw/docs/3.x/migration/module-authors.md

# Source: https://nuxt.com/raw/docs/4.x/migration/module-authors.md

# Modules

> Learn how to migrate from Nuxt 2 to Nuxt 3 modules.

## Module Compatibility

Nuxt 3 has a basic backward compatibility layer for Nuxt 2 modules using `@nuxt/kit` auto wrappers. But there are usually steps to follow to make modules compatible with Nuxt 3 and sometimes, using Nuxt Bridge is required for cross-version compatibility.

We have prepared a [Dedicated Guide](/docs/4.x/guide/modules) for authoring Nuxt 3 ready modules using `@nuxt/kit`. Currently best migration path is to follow it and rewrite your modules. Rest of this guide includes preparation steps if you prefer to avoid a full rewrite yet making modules compatible with Nuxt 3.

<tip icon="i-lucide-puzzle" to="/modules">

Explore Nuxt 3 compatible modules.

</tip>

### Plugin Compatibility

Nuxt 3 plugins are **not** fully backward compatible with Nuxt 2.

<read-more to="/docs/4.x/directory-structure/app/plugins">



</read-more>

### Vue Compatibility

Plugins or components using the Composition API need exclusive Vue 2 or Vue 3 support.

By using [vue-demi](https://github.com/vueuse/vue-demi) they should be compatible with both Nuxt 2 and 3.

## Module Migration

When Nuxt 3 users add your module, you will not have access to the module container (`this.*`) so you will need to use utilities from `@nuxt/kit` to access the container functionality.

### Test with `@nuxt/bridge`

Migrating to `@nuxt/bridge` is the first and most important step for supporting Nuxt 3.

If you have a fixture or example in your module, add `@nuxt/bridge` package to its config (see [example](/docs/4.x/bridge/overview#update-nuxtconfig))

### Migrate from CommonJS to ESM

Nuxt 3 natively supports TypeScript and ECMAScript Modules. Please check [Native ES Modules](/docs/4.x/guide/concepts/esm) for more info and upgrading.

### Ensure Plugins Default Export

If you inject a Nuxt plugin that does not have `export default` (such as global Vue plugins), ensure you add `export default () => { }` to the end of it.

<code-group>

```js [Before]
// ~/plugins/vuelidate.js
import Vue from 'vue'
import Vuelidate from 'vuelidate'

Vue.use(Vuelidate)
```

```js [After]
// ~/plugins/vuelidate.js
import Vue from 'vue'
import Vuelidate from 'vuelidate'

Vue.use(Vuelidate)

export default () => { }
```

</code-group>

### Avoid Runtime Modules

With Nuxt 3, Nuxt is now a build-time-only dependency, which means that modules shouldn't attempt to hook into the Nuxt runtime.

Your module should work even if it's only added to [`buildModules`](/docs/4.x/api/nuxt-config#runtimeconfig) (instead of `modules`). For example:

- Avoid updating `process.env` within a Nuxt module and reading by a Nuxt plugin; use [`runtimeConfig`](/docs/4.x/api/nuxt-config#runtimeconfig) instead.
- (*) Avoid depending on runtime hooks like `vue-renderer:*` for production
- (*) Avoid adding `serverMiddleware` by importing them inside the module. Instead, add them by referencing a file path so that they are independent of the module's context

(*) Unless it is for `nuxt dev` purpose only and guarded with `if (nuxt.options.dev) { }`.

<tip>

Continue reading about Nuxt 3 modules in the [Modules Author Guide](/docs/4.x/guide/modules).

</tip>

### Use TypeScript (Optional)

While it is not essential, most of the Nuxt ecosystem is shifting to use TypeScript, so it is highly recommended to consider migration.

<tip>

You can start migration by renaming `.js` files, to `.ts`. TypeScript is designed to be progressive!

</tip>

<tip>

You can use TypeScript syntax for Nuxt 2 and 3 modules and plugins without any extra dependencies.

</tip>