mediumLow-Level Design

Explain how the EventEmitter class works under the hood.

Q: Explain how the EventEmitter class works under the hood.

**TL;DR.** Internally an EventEmitter keeps a plain object ( _events ) mapping **event name → listener(s)**. .on() pushes a function into that name's array; .emit() looks up the array and calls each listener **synchronously in order** with the emitted args. It's a simple registry, not magic. _events (registry) 'data' [ fn1, fn2 ] — called in order <rect class='d-box-accent

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Describe the implementation structure and logic of the Observer pattern implemented by EventEmitter.

eventemitterpatternsevents

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Synchronous, in-order dispatch

import { EventEmitter } from 'node:events';
const ee = new EventEmitter();

ee.on('x', () => console.log('A'));
ee.on('x', () => console.log('B'));
console.log('before');
ee.emit('x');           // runs A then B synchronously...
console.log('after');   // ...so output is: before, A, B, after

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