Frontend → Node Path

Week 1 learning path (frontend → Node)
Day 1-2  Event loop + non-blocking IO ([How Node.js Works](../node-fundamentals/how-node-js-works/how-node-js-works.md))
Day 3    First Fastify route + Zod + curl smoke
Day 4    node:test integration test with inject()
Day 5    Capstone: POST /items with Postgres + migration

// BAD: blocks event loop ~2s on large sync work
import fs from "node:fs";
const data = fs.readFileSync("./huge.json", "utf8");
JSON.parse(data);
 
// GOOD: async + stream or worker
import fs from "node:fs/promises";
const data = await fs.readFile("./huge.json", "utf8");

import { createReadStream, createWriteStream } from "node:fs";
import { pipeline } from "node:stream/promises";
import { createGzip } from "node:zlib";
 
await pipeline(
  createReadStream("export.csv"),
  createGzip(),
  createWriteStream("export.csv.gz")
);

// test/items.test.ts
import { test } from "node:test";
import assert from "node:assert/strict";
import { buildApp } from "../src/app.js";
 
test("GET /items returns array", async () => {
  const app = await buildApp();
  const res = await app.inject({ method: "GET", url: "/items" });
  assert.equal(res.statusCode, 200);
  assert.ok(Array.isArray(res.json()));
  await app.close();
});

// WRONG: floating promise in fire-and-forget
sendWelcomeEmail(user.id);
 
// RIGHT: await or explicit queue
await emailQueue.add("welcome", { userId: user.id });

await db.transaction(async (tx) => {
  await tx.order.create({ data: order });
  await tx.inventory.decrement({ where: { sku }, data: { qty: 1 } });
});

## Capstone: Items API slice
- [ ] Migration: items table
- [ ] GET /items, POST /items with Zod
- [ ] node:test coverage for 400 and 201
- [ ] curl smoke in PR description
- [ ] No secrets in diff