medusa-store/docs/content/advanced/backend/plugins/create.md

Create a Plugin

In this document, you’ll learn how to create a plugin and publish it. If you’re interested to learn more about what plugins are and where to find available official and community plugins, check out the overview document.

Prerequisites

This guide uses the Medusa CLI throughout different steps. If you don’t have the Medusa CLI installed you can install it with the following command:

npm install @medusajs/medusa-cli -g

Initialize Project

The recommended way to create a plugin is using the Medusa CLI. Run the following command to create a new Medusa project:

medusa new medusa-plugin-custom

Where medusa-plugin-custom is the name of the plugin you’re creating. In Medusa, plugins are named based on their functionalities.

By convention, all plugin names start with medusa followed by a descriptive name of what the plugin does. For example, the Stripe plugin is named medusa-payment-stripe.

Rename Project Name

Update the name field in the package.json file to the name of your plugin. This should be the same name that you chose when running the medusa new command.

Project Structure

The command above creates a new directory medusa-plugin-custom that holds essentially the same codebase you would have for a Medusa server. This is because a plugin has the same directory structure as a Medusa server.

Under the src directory is where the code of your plugin resides. After running the previous command, you should have at least 3 directories inside the src directory:

• api is where you can add custom endpoints.
• services is where you can add custom services.
• subscribers is where you can add custom subscribers.

You can also add more directories and files to your plugin including:

• src/models for adding custom entities or extending existing entities.
• src/migrations for migrations that make changes to the database schema.

Change Dependencies in package.json

A basic Medusa server installed with the medusa new command has dependencies similar to this:

"dependencies": {
  "@medusajs/medusa": "^1.3.1",
  "@medusajs/medusa-cli": "^1.3.0",
  "medusa-fulfillment-manual": "^1.1.31",
  "medusa-interfaces": "^1.3.0",
  "medusa-payment-manual": "^1.0.16",
  "medusa-payment-stripe": "^1.1.38",
  "typeorm": "^0.2.36"
},
"devDependencies": {
  "@babel/cli": "^7.14.3",
  "@babel/core": "^7.14.3",
  "@babel/preset-typescript": "^7.14.5",
  "babel-preset-medusa-package": "^1.1.19"
}

For a plugin, a lot of these dependencies are not necessary or should be labeled as peer dependencies. Therefore, it’s important to make changes to the dependencies of your plugin.

The recommended change is the following:

"peerDependencies": {
  "@medusajs/medusa": "^1.3.1",
  "medusa-interfaces": "^1.3.0",
  "typeorm": "^0.2.36"
},
"devDependencies": {
  "@babel/cli": "^7.14.3",
  "@babel/core": "^7.14.3",
  "@babel/preset-typescript": "^7.14.5",
  "babel-preset-medusa-package": "^1.1.19",
}

The packages @medusajs/medusa and medusa-interfaces act as peer dependencies. They’ll be installed while you develop your package, and they are required when your plugin is installed in another NPM project.

You remove the packages medusa-fulfillment-manual, medusa-payment-manual, and medusa-payment-stripe as they are fulfillment and payment plugins necessary for a Medusa server, but not for a plugin.

Additionally, you remove @medusajs/medusa-cli as you don’t need to use the Medusa CLI while developing a plugin.

Once you’re done making these changes, re-run the install command to update your node_modules directory:

npm install

Recommended Changes in package.json

This section includes recommended changes to your package.json. You can skip any of these changes if you don’t find them necessary to your plugin.

Change Basic Info

package.json holds information that further describes the package or the author that created the package. It is recommended to make the following changes:

• description: Change this to a sentence that describes what your plugin does.
• author: Your name and email.
• repository: The repository that holds your plugin’s codebase.
• keywords: This should hold the keywords that are related to your plugin. It’s recommended that all plugins use the keywords medusa-plugin or medusa.

Change scripts

A basic Medusa installation comes with the following scripts:

"scripts": {
  "seed": "medusa seed -f ./data/seed.json",
  "build": "babel src -d dist --extensions \".ts,.js\"",
  "start": "medusa develop"
}

The seed and start scripts are not necessary for plugin development so you can remove them.

It’s also recommended to add the watch script that automatically compiles your files if they are changed:

"watch": "babel -w src --out-dir . --ignore **/__tests__"

This is helpful when testing the plugin.

:::note

Testing the plugin is covered in a later section.

:::

Another recommended script is the prepare script that builds your files under a “production” environment:

"prepare": "cross-env NODE_ENV=production npm run build"

You would typically run this script before publishing your plugin.

This script requires installing the package cross-env as a development dependency:

npm install --save-dev cross-env

Develop your Plugin

Now, You can start developing your plugin. This can include adding services, endpoints, entities, or anything that is relevant to your plugin.

This guide does not cover how to create each of those files or components. If you’re interested in learning how to do that, you can check out these guides:

• How to create endpoints for storefront and admin
• How to create a service
• How to create a subscriber
• How to create an entity
• How to create a migration

Add Plugin Configuration

Plugins often allow developers that will later use them to enter their own configuration. For example, you can allow developers to specify the API key of a service you’re integrating.

To pass a plugin its configurations on a Medusa server, you have to add it to the plugins array in medusa-config.js:

const plugins = [
  //...
  {
    resolve: `medusa-plugin-custom`,
    options: {
      name: "My Store",
    },
  },
]

Then, you can have access to your plugin configuration in the constructor of services in your plugin:

//In a service in your plugin
constructor({}, options) {
  //options contains plugin configurations
  this.name = options.name
}

You can also have access to the configurations in endpoints in your plugin:

//in an endpoint in your plugin
export default (rootDirectory, options) => {
  //options contain the plugin configurations
  const router = Router()

  router.get("/hello-world", (req, res) => {
    res.json({
      message: `Welcome to ${options.name ? options.name : "Medusa"}!`,
    })
  })

  return router
}

:::tip

Make sure to include in the README of your plugin the configurations that can be passed to a plugin.

:::

Test Your Plugin

While you develop your plugin, you’ll need to test it on an actual Medusa server. This can be done by using the npm link command.

In the root of your plugin directory, run the following command:

npm link

Then, change to the directory of the Medusa server you want to test the plugin on and run the following command:

npm link medusa-plugin-custom

Where medusa-plugin-custom is the package name of your plugin.

After linking to your plugin in a local Medusa server, either run the build or watch commands in your plugin directory:

# in the directory of the plugin
npm run watch

:::tip

If you’re running the watch command, you don’t need to run the build command every time you make a change to your plugin.

:::

Then, add your plugin into the array of plugins in medusa-config.js:

const plugins = [
  //...
  {
    resolve: `medusa-plugin-custom`,
    //if your plugin has configurations
    options: {
      name: "My Store",
    },
  },
]

:::note

If your plugin has migrations, you must run them before you start the server. Check out the Migrations guide for more details.

:::

Finally, start your server and test your plugin’s functionalities:

npm run start

Troubleshoot Errors

Error: The class must be a valid service implementation

Please make sure that your plugin is following the correct structure. If the error persists then please try the following fix:

cd <SERVER_PATH>/node_modules/medusa-interfaces
npm link
cd <PLUGIN_PATH>
rm -rf node_modules/medusa-interfaces
npm link medusa-interfaces
npm link
cd <SERVER_PATH>
npm link your-plugin

Where <SERVER_PATH> is the path to your Medusa server and <PLUGIN_PATH> is the path to your plugin.

This links the medusa-interfaces package from your medusa-backend to your plugin directory and then links your plugin to your medusa-backend.

APIs not loading

If the APIs you added to your Medussa server are not loading then please try the following steps:

cd <PLUGIN_PATH>
rm -rf node_modules
cd <SERVER_PATH>/node_modules/<PLUGIN_NAME>
npm install
cd <PLUGIN_PATH>
npm build
cd <SERVER_PATH>
npm start

Where <SERVER_PATH> is the path to your Medusa server, <PLUGIN_PATH> is the path to your plugin and <PLUGIN_NAME> is the name of your plugin as it is in your plugin package.json file.

:::note

It is safe to ignore any cross-env: command not found error you may receive.

:::

NPM Ignore File

Not all files that you use while developing your plugin are necessary to be published.

For example, the files you add in the src directory are compiled to a dist directory before publishing. Then, when a developer installs your plugin, they’ll just be using the files under the dist directory.

So, you can ignore files and directories like src from the final published NPM package.

To do that, create the file .npmignore with the following content:

/lib
node_modules
.DS_store
.env*
/*.js
!index.js
yarn.lock
src
.gitignore
.eslintrc
.babelrc
.prettierrc

#These are files that are included in a
#Medusa project and can be removed from a
#plugin project
medusa-config.js
Dockerfile
medusa-db.sql
develop.sh

Publish Plugin

Once you’re done developing your plugin you can publish the package on NPM’s registry so that other developers can benefit from it and use it.

Before you publish a plugin, you must create an account on NPM.

Login

In your terminal, log in with your NPM account:

npm login

You’ll be asked to enter your NPM email and password.

Publish Plugin Package

Once you’re logged in, you can publish your package with the following command:

npm publish

Your package is then published on NPM and everyone can use it and install it.

Update Plugin

To update your plugin at a later point, you can run the following command to change the NPM version:

npm version <type>

Where <type> indicates the type of version update you’re publishing. For example, it can be major or minor.

You can see the full list of types in NPM’s documentation.

Then, publish the new update:

npm publish

Add Plugin to Medusa’s Repository

All officially-supported plugins are available in the packages directory of the Medusa GitHub repository.

If you’re interested in adding your plugin, you need to create a new pull request (PR) where you add your plugin inside the packages directory. Our team will then review your plugin, and if it’s approved the PR will be merged and your plugin will be available on Medusa’s repository.

:::note

Before contributing to the Medusa repository, please check out the contribution guidelines.

:::

Install a Plugin

To install any published plugin, you can run the following command on any Medusa server project:

npm install medusa-plugin-custom

What’s Next 🚀

• Check out available Services in Medusa that you can use in your plugin.
• Check out available events that you can listen to in Subscribers.
• Check out available official plugins.