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Node.js Event Emitter

Taslan Graham on August 05, 2021

Node's event-driven architecture allows us to execute certain actions when something happens. This is done via objects (called "emitters") which ca...
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Nitin Sahu •

What are some practical use of event emitters?

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Animesh Jain •

Let's say, when your application starts, you are checking the connection to the database and/or doing some other operations which are in different files and you want to inform your app.js file about the connection or pass the information regarding certain operation in multiple files.
You can send an event across the app and wherever you are listening for that event, you can then perform some other operation like retry if db connection fails.
This is useful for communicating between multiple files, passing data between two js files etc.

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Zulfadhli Zakari •

Do you have any example Express project using event emitter?

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Abby Redwood •

this is effectively what socket.io does.

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rish srivastav •
this snippet is from pdfmake which creates a buffer and stringBase64 

const pdfDoc = printer.createPdfKitDocument(docDefinition);
let chunks = [];
  pdfDoc.on("data", (chunk) => {
    chunks.push(chunk);
  });
  pdfDoc.on("end", () => {
    const result = Buffer.concat(chunks).toString("base64");
    console.log({result})
  });
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Christian Francia •

To drive fellow developers crazy when trying to debug

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sahaj ranipa •

Based on some action you can fire the particular event emitter just say on click certain button you want to fire some event or some code then you can use eventemitter I guess.

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stainlessray •

Home automation would be one. To extend the example from the article - car on, open garage door and turn on the lights.

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Ivan V. • • Edited

Nice article.
For people asking for real world application of the
Event Emitter class, well it enables you to build abstractions like the event bus pattern which enables you to decouple parts of your system (components) or anything else that shouldn't be tightly coupled together.
I've made one such library and wrote an article about it here on dev.
Event Bus Pattern via Native EventEmmiter Class

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yw662 • • Edited

this is exactly the EventTarget we have in DOM, all except on instead of addEventListener, and we can use Element instead.

And, btw, EventTarget is in node.js since 15.

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KAK KOTYAVO! •

I want to say that it is better to use EventEmitter2 as the main solution, since it is really faster.