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How to Create a Plugin

In this document, you’ll learn how to create a plugin and some tips for development. 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.

Alternatively, you can follow this recipe to create a plugin with step-by-step guidance.

Create a PluginLearn how to create a plugin that can be re-used across Medusa backends.
Setup plugin project
Implement Customizations
Change your package.json
Optionally test locally
Publish plugin

Prerequisites​

You must have an existing Medusa project that you want to create the plugin with.

The recommended way to create a plugin is using the new command from Medusa CLI:

npx @medusajs/medusa-cli@latest 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.

Changes to package.json​

Package Name​

By default, your package name in package.json will be medusa-starter-default. This should instead be the name of your plugin. For example, the Stripe plugin's package name is medusa-payment-stripe.

Change Dependencies​

A basic Medusa backend installed with the medusa new command has dependencies that are necessary for the backend, but not necessary for plugins.

For example, can remove the dependencies medusa-fulfillment-manual, medusa-payment-manual, and medusa-payment-stripe as they are fulfillment and payment plugins necessary for a Medusa backend, but not for a plugin. The same goes for modules like @medusajs/cache-inmemory.

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

You should also add @medusajs/medusa as a peer dependency:

"peerDependencies": {
  "@medusajs/medusa": "YOUR_MEDUSA_VERSION",
  // other peer dependencies...
}

Where YOUR_MEDUSA_VERSION is the version you're using of the Medusa core package. You should be able to find it under devDependencies.

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

npm install

Then, make sure to remove the plugins and modules you removed from medusa-config.js:

medusa-config.js
// previously had plugins
const plugins = []

// previously had modules
const modules = {}

Changes for Admin Plugins​

If your plugin contains customizations to the admin dashboard, it's recommended to create different tsconfig files for backend and admin customizations, then modify the scripts in package.json to handle building backend and admin customizations separately.

Note

These changes may already be available in your Medusa project. They're included here for reference purposes.

Start by updating your tsconfig.json with the following configurations:

tsconfig.json
{
  "compilerOptions": {
    "target": "es2019",
    "module": "commonjs",
    "allowJs": true, 
    "checkJs": false, 
    "jsx": "react-jsx", 
    "declaration": true,
    "outDir": "./dist",
    "rootDir": "./src",
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "noEmit": false,
    "strict": false,
    "moduleResolution": "node",
    "esModuleInterop": true,
    "resolveJsonModule": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "include": ["src/"],
  "exclude": [
    "dist",
    "build",
    ".cache",
    "tests",
    "**/*.spec.js",
    "**/*.spec.ts",
    "node_modules",
    ".eslintrc.js"
  ]
}

The important changes to note here are the inclusion of the field "jsx": "react-jsx" and the addition of "build" and “.cache” to exclude.

The addition of "jsx": "react-jsx" specified how should TypeScript transform JSX, and excluding build and .cache ensures that TypeScript ignores build and development files.

Next, create the file tsconfig.server.json with the following content:

tsconfig.server.json
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    /* Emit a single file with source maps instead of having a separate file. */
    "inlineSourceMap": true
  },
  "exclude": ["src/admin", "**/*.spec.js"]
}

This is the configuration that will be used to transpile your custom backend code, such as services or entities. The important part is that it excludes src/admin as that is where your Admin code will live.

Then, create the file tsconfig.admin.json with the following content:

tsconfig.admin.json
{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "module": "esnext"
  },
  "include": ["src/admin"],
  "exclude": ["**/*.spec.js"]
}

This is the configuration that will be used when transpiling your admin code.

Finally, update the build scripts in your project and add a new prepare command:

package.json
"scripts": {
  // other scripts...
  "build": "cross-env npm run clean && npm run build:server && npm run build:admin",
  "build:server": "cross-env npm run clean && tsc -p tsconfig.json",
  "build:admin": "cross-env medusa-admin build",
  "prepare": "cross-env NODE_ENV=production npm run build:server && medusa-admin bundle"
}

Each of these scripts do the following:

  • build: used to build resources for both admin and backend for development. You'll typically use this script during your plugin development.
  • build:server: used to build backend resources for development.
  • build:admin: used to build admin resources for development.
  • prepare: used to build resources for publishing. You'll typically use this script during plugin testing and publishing.

Furthermore, make sure to add react to peerDependencies along with react-router-dom if you're using it:

package.json
"peerDependencies": {
  // other dependencies...
  "react": "^18.2.0",
  "react-router-dom": "^6.13.0"
}

Delete Irrelevant Files​

If you've installed the Medusa backend using the create-medusa-app command, you might find files under the src sub-directories that aren't necessary for your plugin development. For example, src/model/onboarding.ts or migrations under the src/migrations directory.

Make sure to delete these files if you're not using them in your plugin.

Plugin Development​

Plugin Structure​

While developing your plugin, you can create your TypeScript or JavaScript files under the src directory. This includes creating services, API Routes, migrations, and other resources.

However, before you test the changes on a Medusa backend or publish your plugin, you must transpile your files and move them either to a dist directory or to the root of the plugin's directory.

For example, if you have an API Route in src/api/store/custom/route.ts, after running the build or watch commands as defined earlier, the file should be transpiled into dist/api/store/custom/route.ts in your plugin's root. You can alternative transpile them into the api/store/custom/route.ts in your plugin's root.

Development Resources​

This guide doesn't cover how to create different files and components. If you’re interested in learning how to do that, you can check out these guides:

If you're developing something specific, such as a payment processor plugin, you can follow one of the following guides to learn how to create different services within your plugin.

Plugin Options​

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

Developers that use your plugin will pass options to your plugin in the plugins array in medusa-config.js:

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

In your plugin's services, you can have access to the option in their constructor. The options are passed as a second parameter to the constructor method.

For example:

src/service/my.ts
  // In a service in your plugin
class MyService extends TransactionBaseService {
  constructor(container, options) {
    super(container)
    // options contains plugin options
    this.name = options.name
  }
  // ...
}
Tip

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

enableUI Plugin Option​

All plugins accept an option named enableUI. This option is useful mainly if your plugin contains admin customizations. It allows users to enable or disable admin customizations in the admin dashboard.

A developer using your plugin can pass the enableUI option as part of the plugin's options:

medusa-config.js
const plugins = [
  // ...
  {
    resolve: `medusa-plugin-custom`,
    options: {
      // other options
      enableUI: true,
    },
  },
]

If you're passing your plugin options to third-party services, make sure to omit it from the plugin options you receive in your resources, such as services. The enableUI option will always be passed as part of your plugin options.

For example:

src/service/test.ts
  // In a service in your plugin
class MyService extends TransactionBaseService {
  constructor(container, options) {
    super(container)
    // options contains plugin options
    const { enableUI, ...otherOptions } = options
    // pass otherOptions to a third-party service
    const client = new Client(otherOptions)
  }
  // ...
}
Note

enableUI's default value is false if not provided by the plugin users. This means that it must be enabled manually in a plugin's option for the customizations to appear in the admin dashboard.

Test Your Plugin​

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

Step 1: Build Changes​

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

npm run build

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

npm link

Then, in the directory of the Medusa backend you want to test the plugin on, run the following command:

npm link medusa-plugin-custom

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

Step 3: Remove Medusa Dependency​

As your plugin has the @medusajs/medusa package installed, and the Medusa backend has @medusajs/medusa installed as well, this can cause dependency errors.

To avoid that, remove the @medusajs directory from the node_modules of your plugin's directory. For Unix-based operating systems you can use the following command:

rm -rf node_modules/@medusajs

Step 4: Add Plugin to Configurations​

In the medusa-config.js file of the Medusa backend you're testing the plugin on, add your custom plugin to the plugins array:

const plugins = [
  // other plugins...
  {
    resolve: `medusa-plugin-custom`,
    options: {
      // plugin options...
      // if plugin has admin customizations:
      enableUI: true,
    },
  },
]

Make sure to change medusa-plugin-custom with the name of your plugin. Also, if your plugin has admin customizations, make sure to include the enableUI option.

(Optional) Step 5: Run Migrations​

If your plugin includes migrations, run the following command in the Medusa backend's directory:

npx medusa migrations run

Step 6: Run the Medusa Backend​

In the directory of the Medusa backend, start the backend with the dev command passing it the --preserve-symlinks option:

npm run dev -- -- --preserve-symlinks

Making Changes to the Plugin​

While testing your plugin, if you need to make changes you need to re-install the plugin's dependencies:

npm install

Then, after making the changes, run the steps one, three, and six mentioned above.

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 <BACKEND_PATH>/node_modules/medusa-interfaces
npm link
cd <BACKEND_PATH>/node_modules/@medusajs/medusa
npm link
cd <PLUGIN_PATH>
rm -rf node_modules/medusa-interfaces
rm -rf node_modules/@medusajs/medusa
npm link medusa-interfaces
npm link @medusajs/medusa
npm link
cd <BACKEND_PATH>
npm link your-plugin

Where <BACKEND_PATH> is the path to your Medusa backend and <PLUGIN_PATH> is the path to your plugin.

This links the medusa-interfaces and @medusajs/medusa packages 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 backend are not loading then please try the following steps:

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

Where <BACKEND_PATH> is the path to your Medusa backend, <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.

Publish Plugin​

Once you're done with the development of the plugin, you can publish it to NPM so that other Medusa developers and users can use it.

Please refer to this guide on required steps to publish a plugin.

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