Subscribers
In this document, you'll learn what Subscribers are in Medusa.
What are Events
In Medusa, there are events that are emitted when a certain action occurs. For example, if a customer places an order, the order.placedCopy to Clipboard event is emitted with the order data.
The purpose of these events is to allow other parts of the platform, or third-party integrations, to listen to those events and perform a certain action. That is done by creating subscribers.
Medusa's queuing and events system is handled by Redis. So, you must have Redis configured on your server to use subscribers.
What are Subscribers
Subscribers register handlers for an events and allows you to perform an action when that event occurs. For example, if you want to send your customer an email when they place an order, then you can listen to the order.placedCopy to Clipboard event and send the email when the event is emitted.
Natively in Medusa there are subscribers to handle different events. However, you can also create your own custom subscribers.
Custom subscribers are TypeScript or JavaScript files in your project's src/subscribersCopy to Clipboard directory. Files here should export classes, which will be treated as subscribers by Medusa. By convention, the class name should end with SubscriberCopy to Clipboard and the file name should be the camel-case version of the class name without SubscriberCopy to Clipboard. For example, the WelcomeSubscriberCopy to Clipboard class is in the file src/subscribers/welcome.tsCopy to Clipboard.
Whenever an event is emitted, the subscriber’s registered handler method is executed. The handler method receives as a parameter an object that holds data related to the event. For example, if an order is placed the order.placedCopy to Clipboard event will be emitted and all the handlers will receive the order id in the parameter object.
Example Use Cases
Subscribers are useful in many use cases, including:
- Send a confirmation email to the customer when they place an order by subscribing to the
order.placedCopy to Clipboard event. - Automatically assign new customers to a customer group by subscribing to the
customer.createdCopy to Clipboard. - Handle custom events that you emit