Nuxt/docs/content/migration/20.module-authors.md

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---
head.title: 'Nuxt 2 to Nuxt 3: Modules'
head.titleTemplate: ''
---
# 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](/guide/going-further/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 compatibile with Nuxt 3.
::alert
You can check for a list of Nuxt 3 ready modules from [Nuxt Modules](https://modules.nuxtjs.org/?version=3.x).
::
### Plugin Compatibility
Nuxt 3 plugins are **not** fully backward compatible with Nuxt 2.
### 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, a compatible module container layer from `@nuxt/kit` is **automatically injected**, so as long as your code is following the guidelines below, it should continue working as-is.
### 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](/bridge#update-nuxtconfig))
### Migrate from CommonJS to ESM
Nuxt 3 natively supports TypeScript and ECMAScript Modules. Please check [Native ES Modules](/guide/going-further/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 () => { }
```
::
### 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`](/guide/directory-structure/nuxt.config#buildmodules) (instead of `modules`). For example:
- Avoid updating `process.env` within a Nuxt module and reading by a nuxt plugin; use [`runtimeConfig`](/guide/directory-structure/nuxt.config#publicruntimeconfig) 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) { }`.
::alert{type=info icon=🔎}
Continue reading about Nuxt 3 modules in the [Modules guide](/guide/going-further/modules).
::
### 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.
::alert{icon=💡}
You can start migration by renaming `.js` files, to `.ts`. TypeScript is designed to be progressive!
::
::alert{icon=💡}
You can use TypeScript syntax for Nuxt 2 and 3 modules and plugins without any extra dependencies.
::