1// Common Node.js performance optimizations
2 
3// ❌ Anti-pattern: Sequential DB calls (100ms + 100ms = 200ms)
4async function getDashboardSlow(userId: string) {
5  const user = await db.users.findById(userId);              // 50ms
6  const orders = await db.orders.getByUserId(userId);        // 50ms
7  const analytics = await db.analytics.getUserStats(userId); // 100ms
8  return { user, orders, analytics };                         // Total: 200ms
9}
10 
11// ✅ Parallel DB calls (max(50, 50, 100) = 100ms)
Promise.all: 3 independent queries start simultaneously. Total = max(50, 50, 100) = 100ms vs 200ms
12async function getDashboardFast(userId: string) {
13  const [user, orders, analytics] = await Promise.all([
14    db.users.findById(userId),
15    db.orders.getByUserId(userId),
16    db.analytics.getUserStats(userId),
17  ]);
18  return { user, orders, analytics };                         // Total: 100ms
19}
20 
21// ❌ Anti-pattern: Serializing huge datasets blocks event loop
JSON.stringify on 100k objects blocks the event loop for seconds — all other requests stall
22app.get('/export', async (req, res) => {
23  const data = await db.getAllRows();    // 100k rows
24  res.json(data);                       // JSON.stringify blocks event loop for 2s!
25});
26 
Streaming: serialize row-by-row, never holding full dataset in memory or blocking the loop
27// ✅ Streaming: serialize row-by-row, event loop never blocks
28app.get('/export', async (req, res) => {
29  res.setHeader('Content-Type', 'application/json');
30  res.write('[');
31  let first = true;
32 
33  for await (const row of db.streamAllRows()) {
34    if (!first) res.write(',');
35    res.write(JSON.stringify(row));  // one row at a time
36    first = false;
37  }
38 
39  res.write(']');
40  res.end();
Worker threads: CPU-intensive work runs in a separate thread, event loop stays free for requests
41});
42 
43// ✅ CPU-intensive work → Worker Thread (never blocks event loop)
44import { Worker } from 'worker_threads';
45 
46function runInWorker(data: unknown): Promise<unknown> {
47  return new Promise((resolve, reject) => {
48    const worker = new Worker('./heavy-computation.js', { workerData: data });
49    worker.on('message', resolve);
50    worker.on('error', reject);
51  });
52}
53 
54const result = await runInWorker({ imageBuffer: req.file.buffer });