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What are `EventEmitter`s in Node.js?

Q: What are `EventEmitter`s in Node.js?

**TL;DR.** EventEmitter (from node:events ) is the core class behind Node's **event-driven** model. Objects **emit named events** ( emitter.emit('data', payload) ) and **listeners** registered with .on() react to them. Streams, HTTP servers, sockets, and the process object all inherit from it. EventEmitter emit('data') <t

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A fundamental pattern for event-driven programming.

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Define and use an emitter

import { EventEmitter } from 'node:events';

class Job extends EventEmitter {}
const job = new Job();

job.on('progress', (pct) => console.log('progress', pct));
job.once('done', (r) => console.log('done', r));
job.on('error', (e) => console.error('handled:', e.message)); // always add!

job.emit('progress', 50);
job.emit('done', { ok: true });

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