What is the Node.js architecture?

Direct answer

Node layers JavaScript user code on Node bindings (C++), libuv for the event loop and async I/O, and V8 for execution — with optional worker threads and child processes for parallelism outside the main loop.

A complete mental model stacks four pieces: your JS → Node core modules (written in JS + C++) → libuv → operating system kernel.

Application layer — Express/Fastify routes, your business logic, npm packages.
Node API surface — fs, http, crypto, stream wrappers exposing libuv to JavaScript.
libuv — event loop, thread pool, cross-platform polling (Q8–9).
V8 — executes JS and calls into bindings when you invoke node:fs.readFile.

architecture-flow.js

import http from "node:http";
import fs from "node:fs";

// JS handler
const server = http.createServer((req, res) => {
  // Binding → libuv async read → callback when ready
  fs.readFile("./data.json", (err, buf) => {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(buf);
  });
});

server.listen(4000);