Modules, Runtime & Tooling

Node.js Runtime & Evented I/O

Node.js runs JavaScript outside the browser and provides host APIs for files, networking, processes, diagnostics, packages, and server-side execution. Its I/O model is evented: many operations are asynchronous so the process can keep handling other work.

Node is a runtime, not the language
Evented I/O keeps one process responsive
CPU-heavy JavaScript still blocks the event loop
Node has browser-like APIs but not a browser environment
Operational Node code needs runtime discipline

Node runtime layers

The language is only one layer; Node adds runtime APIs and OS integration.

Async file I/O

import { readFile } from "node:fs/promises"

export async function readConfig(path: string) {
  const text = await readFile(path, "utf8")
  return JSON.parse(text) as unknown
}

The file operation is asynchronous; parsing is synchronous and can still throw.

Node vs language concepts
Concept	Owned by	Example
Syntax and semantics	ECMAScript	let, class, Promise, modules
Engine	V8	Parses and executes JavaScript
Runtime APIs	Node	fs, process, Buffer, streams
Package tooling	Node/npm ecosystem	npm scripts, node_modules
OS integration	Host system	signals, sockets, files