The EventEmitter Pattern

emit and on

Create an emitter, subscribe with on, fire an event with emit.

import { EventEmitter } from "node:events";

const orders = new EventEmitter();

orders.on("placed", (item) => {
  console.log(`Order received: ${item}`);
});

orders.emit("placed", "Laptop");

Output:

Order received: Laptop

A radio station

An EventEmitter is like a radio station: it broadcasts (emit), and any number of listeners can tune in (on) without the station knowing who they are.

Core Node runs on it

HTTP servers, streams, and process itself are all EventEmitters under the hood — request, data, close are all events.