Lesson 25 — Full event emitter

on, off and emit

A full event emitter has three methods: on(event, fn) registers a listener, off(event, fn) removes it, emit(event, data) calls every listener of that event. Removing works by keeping all functions except the one you pass — that is why you must keep a reference to the handler (const h = ...).

[1, 2, 3].filter((x) => x !== 2);   // [1, 3]

Why it matters: events let parts of an app talk without knowing about each other — the core of Node and the browser DOM.