This process will also show how to manage erroneous events from the emitter and how to manage event subscribers. We will set up listeners for the buy event, which will trigger every time a ticket is bought. In this article, we will create an event listener for a TicketManager JavaScript class that allows a user to buy tickets. If we wanted to change the behavior of our application, we could adjust how the subscribers react to the events without having to change the publisher. A publisher publishes a message, and it’s up to the subscribers to react to it in their respective ways. The power of this pattern is that the publisher does not need to know about the subscribers. In this software architecture pattern, a publisher (the event emitter) sends a message (an event), and a subscriber receives the event and performs an action. Event emitters provide a different way to structure this relationship: the publish-subscribe pattern. However, these techniques tightly couple the triggering action and the resulting action, making it difficult to modify the resulting action in the future. Typically in Node.js, when we want to have an action occur upon completion of another action, we use asynchronous programming techniques like nesting callbacks or chaining promises. In this context, events are composed of an identifying string and any data that needs to be passed to the listeners. JavaScript developers can write code that listens to events from an event emitter, allowing them to execute functions every time those events are triggered.

IntroductionĮvent emitters are objects in Node.js that trigger an event by sending a message to signal that an action was completed. The author selected the COVID-19 Relief Fund to receive a donation as part of the Write for DOnations program.

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