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Node event emitter

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by Abdul Rawoof A R dot icon Updated: Jan 31, 2024

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The 'EventEmitter' is a class. It helps us create a publisher-subscriber pattern in Node.js. We can raise a new event from various parts of an application. 


A listener will listen to the raise event with an event emitter. We have some actions to perform for the event.  An event emitter is a pattern that listens to a named event, fires a callback, and then emits that event with a value. If we add the new listener, then we fire the new listener event. When we remove the listener, it fires the removeListener event. This event provides us with many properties, such as on and emit. In Node, the property binds a function with the event. The module facilitates communication/interaction between objects by firing an event using emit. The event emitter is at the core of Node's asynchronous, event-driven architecture. Many of Node's built-in modules are inherited from EventEmitter. Prominent frameworks like Express.js also do this.   



Here is an example of a node event emitter: 

Fig: Preview of the output that you will get on running this code from your IDE.

Code

Node event emitter

JavaScriptdotLines of Code : 18dotLicense : Strong Copyleft (CC BY-SA 4.0)

const fs = require("fs");

var writeStream = fs.createWriteStream("demo.txt");
writeStream.write('some data','UTF8');
writeStream.end();
writeStream.on('finish',function(){
  console.log("finish");

  let data = '';

  const read = fs.createReadStream("demo.txt", {encoding: 'UTF8'});

  read.on('data', function(resp) {  
    console.log(resp);
    data += resp;
  });
});

Instructions

Follow the steps carefully to get the output easily.

  1. Install Node and Visual Studio Code on your computer.
  2. Create a new folder in your local.
  3. Open that folder in Visual Studio Code.
  4. Then create a new JS file(Eg: node.js).
  5. Copy the snippet using 'copy' button and paste it into that file.
  6. Save the file and open the terminal, use this command 'node filename(node.js)' to get the output in your console.


I hope you found this helpful.


I found this code snippet by searching for 'node event emitter' in kandi. You can try any such use case!

Environment Tested

I tested this solution in the following versions. Be mindful of changes when working with other versions.

  1. The solution is created and tested in Visual Studio Code 1.74.1.
  2. The solution is tested in Node v18.15.0.


Using this solution, we are able to implement node event emitter with simple steps. This process also facilities an easy way to use, hassle-free method to create a hands-on working version of code which would help us to implement node event emitter.

FAQ 

1. What is an EventEmitter in Node.js? 

An EventEmitter in Node.js is like a messenger that helps different parts of a program talk to each other. It lets you create a system where one part can let others know when something important happens. Other parts can listen and respond to those events. 


2. How does EventEmitter work? 

Think of EventEmitter as a radio station. When something interesting occurs, it broadcasts a message. Anyone who tunes in (listens) can hear that message and react. It's a way for different pieces of your program to stay informed and act when needed. 


3. What's the purpose of "on" and "emit" in EventEmitter? 

"on" is like subscribing to a newsletter. You tell the EventEmitter, "Hey, when this specific event happens, do something. "emit" is like sending out that newsletter. It says, "Hey, this event happened, and anyone who subscribed should do their thing now. 


4. Why is EventEmitter important in Node.js? 

Node.js, built on an event-driven architecture, relies on EventEmitter at its heart. It permits distinctive components of software to communicate. This makes Node.js great for handling many tasks. It doesn't wait for one to finish before starting another. 


5. Can you explain the newListener and removeListener events in EventEmitter? 

Think of these events as notifications about people joining or leaving a club. Adding a brand-new listener triggers the "new listener" event. When someone leaves (removes a listener), it triggers the "removeListener" event. It helps you keep track of who's paying attention to your events. 

 

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