87 lines
3.3 KiB
Markdown
87 lines
3.3 KiB
Markdown
---
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description: 'Learn how to create a loader in Medusa. A loader can be created in the Medusa backend codebase, in a plugin, or in a module.'
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addHowToData: true
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---
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# How to Create a Loader
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In this document, you’ll learn how to create a loader in Medusa. A loader can be created in the Medusa backend codebase, in a plugin, or in a module.
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## Step 1: Create Loader File
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Create a TypeScript or JavaScript file in the `src/loaders` directory that will hold your custom script. There are no restrictions on the name of the file.
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For example, create the file `src/loaders/my-loader.ts` that will hold the loader.
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---
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## Step 2: Define the Loader
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The loader file must export a function.
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### Parameters of Loaders in Medusa Backend and Plugins
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When the loader is defined in the Medusa backend or a plugin, the function receives the following parameters:
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1. `container`: the first parameter, which is a `AwilixContainer` object. You can use the container to register custom resources into the dependency container or resolve resources from the dependency container.
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2. `config`: the second parameter, which is an object that holds the loader’s plugin options. If the loader is not created inside a plugin, the config object will be empty.
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### Parameters of Loaders in Modules
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When the loader is defined in a module, it receives the following parameters:
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1. `container`: the first parameter, which is a `AwilixContainer` object. You can use the container to register custom resources into the dependency container or resolve resources from the dependency container.
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2. `logger`: the second parameter, which is a `Logger` object. The logger can be used to log messages in the console.
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3. `config`: the third parameter, which is an object that holds the loader’s module options.
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### Example Implementation
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For example, this loader function resolves the `ProductService` and logs in the console the count of products in the Medusa backend:
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```ts title=src/loaders/my-loader.ts
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import { ProductService } from "@medusajs/medusa"
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import { AwilixContainer } from "awilix"
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export default async (
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container: AwilixContainer,
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config: Record<string, unknown>
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): Promise<void> => {
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console.info("Starting loader...")
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const productService = container.resolve<ProductService>(
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"productService"
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)
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console.info(`Products count: ${
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await productService.count()
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}`)
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console.info("Ending loader...")
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}
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```
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---
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## Step 3: Run Build Command
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In the directory of your project, run the following command to transpile the files from the `src` to the `dist` directory:
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```bash npm2yarn
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npm run build
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```
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---
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## Test it Out
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:::note
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This section explains how to test out the loader if it’s created in the Medusa backend codebase. If you’re creating your loader in a plugin, you can learn how to test it in the [plugins documentation](../plugins/create.mdx#test-your-plugin). Alternatively, if you’re creating your loader in a module, you can learn how to test it in the [modules documentation](../modules/create.mdx#step-4-test-your-module).
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:::
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Run the following command to start the Medusa backend:
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```bash npm2yarn
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npx @medusajs/medusa-cli develop
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```
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Your loader script should run on the Medusa backend startup. If you logged a message in the console, similar to the example above, you should see it in the console.
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