Node.js Roadmap
scratch to advanced.

// package.json: { "type": "module" }
import http from "node:http";

const server = http.createServer((req, res) => {
  res.writeHead(200, { "Content-Type": "application/json" });
  res.end(JSON.stringify({ ok: true, path: req.url }));
});

server.listen(3000, () => {
  console.log("Listening on http://localhost:3000");
});

import { readFile } from "node:fs/promises";
import path from "node:path";
import { fileURLToPath } from "node:url";

const __dirname = path.dirname(fileURLToPath(import.meta.url));
const configPath = path.join(__dirname, "config.json");

const raw = await readFile(configPath, "utf8");
const config = JSON.parse(raw);
console.log(config.port ?? 3000);

import express from "express";

const app = express();
app.use(express.json());

app.get("/api/health", (_req, res) => {
  res.json({ status: "ok" });
});

app.post("/api/messages", (req, res) => {
  const { email, body } = req.body ?? {};
  if (!email || !body) {
    return res.status(400).json({ error: "email and body required" });
  }
  // persist to database...
  res.status(201).json({ id: "msg_1" });
});

app.use((err, _req, res, _next) => {
  console.error(err);
  res.status(500).json({ error: "Internal server error" });
});

app.listen(3000);

import { createReadStream, createWriteStream } from "node:fs";
import { pipeline } from "node:stream/promises";

await pipeline(
  createReadStream("large-input.csv"),
  createWriteStream("large-output.csv"),
);
console.log("Copy complete without loading entire file into RAM");

import pg from "pg";

const pool = new pg.Pool({ connectionString: process.env.DATABASE_URL });

export async function findUserByEmail(email) {
  const { rows } = await pool.query(
    "SELECT id, email, name FROM users WHERE email = $1 LIMIT 1",
    [email],
  );
  return rows[0] ?? null;
}

const required = ["DATABASE_URL", "JWT_SECRET", "NODE_ENV"];

for (const key of required) {
  if (!process.env[key]) {
    throw new Error(`Missing required environment variable: ${key}`);
  }
}

// Fail fast at startup — not on the first user request

import request from "supertest";
import { describe, it, expect } from "vitest";
import { app } from "./app.js";

describe("GET /api/health", () => {
  it("returns 200", async () => {
    const res = await request(app).get("/api/health");
    expect(res.status).toBe(200);
    expect(res.body.status).toBe("ok");
  });
});

import http from "node:http";

const server = http.createServer(app);
server.listen(3000);

function shutdown(signal) {
  console.log(`${signal} received — closing server`);
  server.close(() => {
    pool.end().then(() => process.exit(0));
  });
}

process.on("SIGTERM", () => shutdown("SIGTERM"));
process.on("SIGINT", () => shutdown("SIGINT"));