Nuxt/docs/content/2.guide/4.going-further/3.modules.md

# Module Author Guide

Nuxt provides a zero-config experience with a preset of integrations and best practices to develop Web applications.
A powerful configuration and hooks system makes it possible to customize almost every aspect of Nuxt Framework and add endless possible integrations when it comes to customization. You can learn more about how Nuxt works in the [Nuxt internals](/guide/going-further/internals) section.

Nuxt exposes a powerful API called **Nuxt Modules**. Nuxt modules are simple async functions that sequentially run when starting Nuxt in development mode using `nuxi dev` or building a project for production with `nuxi build`.
Using Nuxt Modules, we can encapsulate, properly test and share custom solutions as npm packages without adding unnecessary boilerplate to the Nuxt project itself.
Nuxt Modules can hook into lifecycle events of Nuxt builder, provide runtime app templates, update the configuration or do any other custom action based on needs.

## Quick Start

For the impatient ones, You can quickly start with [module-builder](https://github.com/nuxt/module-builder) and [module starter template](https://github.com/nuxt/starter/tree/module):

```bash
npx nuxi init -t module my-module
```

Starter template and module starter is a standard path of creating a Nuxt module.

**Next steps:**

1. Open `my-module` in the IDE of your choice (Visual Studio Code is recommended)
2. Install dependencies using the package manager of your choice (Yarn is recommended)
3. Ensure local files are generated using `npm run dev:prepare`
4. Start playground using `npm run dev`
5. Follow this document to learn more about Nuxt modules

::alert{type=info icon=🚧}
This is an under-the-progress guide. Please regularly check for updates.
::

## Module Anatomy

A Nuxt module is a simple function accepting inline user options and `nuxt` arguments.

It is totally up to you, as the module author, how to handle the rest of the logic.

Starting with Nuxt 3, modules can benefit all [Nuxt Kit](/api/advanced/kit) utilities.

```ts [modules/example.ts]
// modules/module.mjs
export default async (inlineOptions, nuxt) => {
  // You can do whatever you like here..
  console.log(inlineOptions.token) // `123`
  console.log(nuxt.options.dev) // `true` or `false`
  nuxt.hook('ready', async nuxt => {
    console.log('Nuxt is ready')
  })
}
```

```ts [nuxt.config]
export default defineNuxtConfig({
  modules: [
    // Using package name (recommended usage)
    '@nuxtjs/example',

    // Load a local module
    './modules/example',

    // Add module with inline-options
    ['./modules/example', { token: '123' }]

    // Inline module definition
    async (inlineOptions, nuxt) => { }
  ]
})
```

## Defining Nuxt Modules

Creating Nuxt modules involves tedious and common tasks. [Nuxt Kit](/api/advanced/kit), provides a convenient and standard API to define Nuxt modules using `defineNuxtModule`:

```js
import { defineNuxtModule } from '@nuxt/kit'

export default defineNuxtModule({
  meta: {
    // Usually  npm package name of your module
    name: '@nuxtjs/example',
    // The key in `nuxt.config` that holds your module options
    configKey: 'sample',
    // Compatibility constraints
    compatibility: {
      // Semver version of supported nuxt versions
      nuxt: '^3.0.0'
    }
  },
  // Default configuration options for your module
  defaults: {},
  hooks: {},
  async setup(moduleOptions, nuxt) {
    // -- Add your module logic here --
  }
})
```

The result of `defineNuxtModule` is a wrapper function with an `(inlineOptions, nuxt)` signature. It applies defaults and other necessary steps and calls the `setup` function when called.

**`defineNuxtModule` features:**

::list

- Support `defaults` and `meta.configKey` for automatically merging module options
- Type hints and automated type inference
- Add shims for basic Nuxt 2 compatibility
- Ensure module gets installed only once using a unique key computed from `meta.name` or `meta.configKey`
- Automatically register Nuxt hooks
- Automatically check for compatibility issues based on module meta
- Expose `getOptions` and `getMeta` for internal usage of Nuxt
- Ensuring backward and upward compatibility as long as the module is using `defineNuxtModule` from the latest version of `@nuxt/kit`
- Integration with module builder tooling

::

## Best Practices

### Async Modules

Nuxt Modules can do asynchronous operations. For example, you may want to develop a module that needs fetching some API or calling an async function.

::alert{type="warning"}
Be careful that `nuxi dev` waits for your module setup before going to the next module and starting the development server. Do time-consuming logic using deferred Nuxt hooks.
::

### Always Prefix Exposed Interfaces

Nuxt Modules should provide an explicit prefix for any exposed configuration, plugin, API, composable, or component to avoid conflict with other modules and internals.

Ideally, you should prefix them with your module's name (e.g. if your module is called `nuxt-foo`, expose `<FooButton>` and `useFooBar()` and **not** `<Button>` and `useBar()`).

### Be TypeScript Friendly

Nuxt 3, has first-class typescript integration for the best developer experience.

Exposing types and using typescript to develop modules can benefit users even when not using typescript directly.

### Avoid CommonJS Syntax

Nuxt 3, relies on native ESM. Please read [Native ES Modules](/guide/going-further/esm) for more information.

## Modules Ecosystem

Nuxt tends to have a healthy and rich ecosystem of Nuxt modules and integrations. Here are some best practices if you want to jump in and contribute!

### Document Module Usage

Consider documenting module usage in the readme file:

- Why use this module
- How to use this module
- What this module does?

Linking to the integration website and documentation is always a good idea.

### Use `nuxt-` Prefix for npm Packages

To make your modules discoverable, use `nuxt-` prefix for the npm package name. This is always the best starting point to draft and try an idea!

### Listing Module on modules.nuxtjs.org

Do you have a working Module and want it listed on [modules.nuxtjs.org](https://modules.nuxtjs.org)? Open an issue in [nuxt/modules](https://github.com/nuxt/modules/issues/new) repository.
Nuxt team can help you to apply best practices before listing.

### Do Not Advertize With a Specific Nuxt Version

Nuxt 3, Nuxt Kit, and other new toolings are made to have both forward and backward compatibility in mind.

Please use "X for Nuxt" instead of "X for Nuxt 3" to avoid fragmentation in the ecosystem and prefer using `meta.compatibility` to set Nuxt version constraints.

### Joining nuxt-community

By moving your modules to [nuxt-community](https://github.com/nuxt-community), there is always someone else to help, and this way, we can join forces to make one perfect solution.

If you have an already published and working module and want to transfer it to nuxt-community, open an issue in [nuxt/modules](https://github.com/nuxt/modules/issues/new).

## Testing

### `@nuxt/test-utils`

Nuxt 3 has a testing library for testing Nuxt apps and modules. You can check out [testing modules](/getting-started/testing#testing-modules) for more information and examples.

### Testing Externally

If you wish to test your module outside of the module playground before publishing to npm, you can use [`npm pack`](https://docs.npmjs.com/cli/v7/commands/npm-pack) command, or your package manager equivalent, to create a tarball from your module. Then in your test project, you can add your module to `package.json` packages as: `"nuxt-module-name": "file:/path/to/tarball.tgz"`.

After that, you should be able to reference `nuxt-module-name` like in any regular project.

## Examples

### Provide Nuxt Plugins

Commonly, modules provide one or more run plugins to add runtime logic.

```ts
import { defineNuxtModule, addPlugin, createResolver } from '@nuxt/kit'

export default defineNuxtModule<ModuleOptions>({
  setup (options, nuxt) {
    // Create resolver to resolve relative paths
    const { resolve } = createResolver(import.meta.url)

    addPlugin(resolve('./runtime/plugin'))
  }
})
```

::ReadMore{link="/api/advanced/kit" title="API > Advanced > Kit"}
::

### Add a CSS Library

If your module will provide a CSS library, make sure to check if the user already included the library to avoid duplicates and add an option to disable the CSS library in the module.

```ts
import { defineNuxtModule } from '@nuxt/kit'

export default defineNuxtModule({
  setup (options, nuxt) {
    nuxt.options.css.push('font-awesome/css/font-awesome.css')
  }
})
```

### Adding Vue Components

If your module should provide Vue components, you can use the `addComponent` utility to add them as auto-imports for Nuxt to resolve.

```ts
import { defineNuxtModule, addComponent } from '@nuxt/kit'

export default defineNuxtModule({
  setup(options, nuxt) {
    addComponent({
      name: 'MyComponent', // name of the component to be used in vue templates
      export: 'MyAwesomeComponent', // (optional) if the component is a named (rather than default) export
      // filePath should be package name or resolved path
      // if the component is created locally, preferably in `runtime` dir
      filePath: '@vue/awesome-components' // resolve(runtimeDir, 'components', 'MyComponent.vue')
    })
  }
})
```

### Clean Up Module

If your module opens, handles or starts a watcher, you should close it when the Nuxt lifecycle is done. For this, use the `close` hook:

```ts
import { defineNuxtModule } from '@nuxt/kit'

export default defineNuxtModule({
  setup (options, nuxt) {
    nuxt.hook('close', async nuxt => {
      // Your custom code here
    })
  }
})
```