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78 lines
2.4 KiB
Markdown
78 lines
2.4 KiB
Markdown
---
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description: 'Learn how to add a middleware in Medusa. A middleware is a function that has access to the request and response objects and can be used to perform actions around an endpoint.'
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addHowToData: true
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---
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# How to Add a Middleware
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In this document, you’ll learn how to add a middleware to an existing or custom route in Medusa.
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## Overview
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As the Medusa server is built on top of [Express](https://expressjs.com/), Express’s features can be utilized during your development with Medusa.
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One feature in particular is adding a [middleware](http://expressjs.com/en/guide/using-middleware.html#using-middleware). A middleware is a function that has access to the request and response objects.
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A middleware can be used to perform an action when an endpoint is called or modify the response, among other usages.
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You can add a middleware to an existing route in the Medusa server, a route in a plugin, or your custom routes.
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---
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## Add a Middleware
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Adding a middleware is very similar to adding a custom endpoint. The middleware must be created either in the `src/api/index.ts` entry point, or other TypeScript or JavaScript files imported into `src/api/index.ts`.
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:::info
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Learn more about creating custom endpoints in [this documentation](./add.md).
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:::
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The following code snippet is an example of adding a middleware:
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```ts title=src/api/index.ts
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import { Router } from "express"
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export default () => {
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const router = Router()
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router.use("/store/products", (req, res, next) => {
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// / perform an action when retrieving products
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next()
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})
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return router
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}
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```
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This code snippet adds a middleware to the [List Products](/api/store/#tag/Product/operation/GetProducts) endpoint. In the middleware function, you can perform any action.
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Then, you must call the `next` method received as a third parameter in the middleware function to ensure that the endpoint executes after the middleware.
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:::info
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You can learn more about Middlewares and their capabilities in [Express’s documentation](http://expressjs.com/en/guide/using-middleware.html#using-middleware).
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:::
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---
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## Building Files
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Similar to custom endpoints, you must transpile the files under `src` into the `dist` directory for the server to load them.
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To do that, run the following command before running the Medusa server:
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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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## See Also
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- [Create an Endpoint](./add.md)
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- [Store API reference](/api/store)
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- [Admin API reference](/api/admin)
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