{"id":4398,"date":"2025-08-09T06:52:17","date_gmt":"2025-08-09T06:52:17","guid":{"rendered":"https:\/\/uplatz.com\/blog\/?p=4398"},"modified":"2025-08-09T08:06:01","modified_gmt":"2025-08-09T08:06:01","slug":"node-js-pocket-book","status":"publish","type":"post","link":"https:\/\/uplatz.com\/blog\/node-js-pocket-book\/","title":{"rendered":"Node.js Pocket Book"},"content":{"rendered":"<p><!-- Node.js Pocket Book \u2014 Uplatz (50 Cards, Wide Layout, Readable Code, Scoped Styles) --><\/p>\n<div style=\"margin: 16px 0;\">\n<style>\n    .wp-nodejs-pb { font-family: Arial, sans-serif; max-width: 1320px; margin:0 auto; }\n    .wp-nodejs-pb .heading{\n      background: linear-gradient(135deg, #e0f2fe, #ccfbf1); \/* lighter gradient *\/\n      color:#0f172a; padding:22px 24px; border-radius:14px;\n      text-align:center; margin-bottom:18px; box-shadow:0 8px 20px rgba(0,0,0,.08);\n      border:1px solid #cbd5e1;\n    }\n    .wp-nodejs-pb .heading h2{ margin:0; font-size:2.1rem; letter-spacing:.2px; }\n    .wp-nodejs-pb .heading p{ margin:6px 0 0; font-size:1.02rem; opacity:.9; }<\/p>\n<p>    \/* Wide, dense grid *\/\n    .wp-nodejs-pb .grid{\n      display:grid; gap:14px;\n      grid-template-columns: repeat(auto-fill, minmax(400px, 1fr));\n    }\n    @media (min-width:1200px){\n      .wp-nodejs-pb .grid{ grid-template-columns: repeat(3, 1fr); }\n    }<\/p>\n<p>    .wp-nodejs-pb .section-title{\n      grid-column:1\/-1; background:#f8fafc; border-left:8px solid #0ea5e9;\n      padding:12px 16px; border-radius:10px; font-weight:700; color:#0f172a; font-size:1.08rem;\n      box-shadow:0 2px 8px rgba(0,0,0,.05); border:1px solid #e2e8f0;\n    }\n    .wp-nodejs-pb .card{\n      background:#ffffff; border-left:6px solid #0ea5e9;\n      padding:18px; border-radius:12px;\n      box-shadow:0 6px 14px rgba(0,0,0,.06);\n      transition:transform .12s ease, box-shadow .12s ease;\n      border:1px solid #e5e7eb;\n    }\n    .wp-nodejs-pb .card:hover{ transform: translateY(-3px); box-shadow:0 10px 22px rgba(0,0,0,.08); }\n    .wp-nodejs-pb .card h3{ margin:0 0 10px; font-size:1.12rem; color:#0f172a; }\n    .wp-nodejs-pb .card p{ margin:0; font-size:.96rem; color:#334155; line-height:1.62; }<\/p>\n<p>    \/* Color helpers *\/\n    .bg-blue { border-left-color:#0ea5e9 !important; background:#f0f9ff !important; }\n    .bg-green{ border-left-color:#10b981 !important; background:#f0fdf4 !important; }\n    .bg-amber{ border-left-color:#f59e0b !important; background:#fffbeb !important; }\n    .bg-violet{ border-left-color:#8b5cf6 !important; background:#f5f3ff !important; }\n    .bg-rose{ border-left-color:#ef4444 !important; background:#fff1f2 !important; }\n    .bg-cyan{ border-left-color:#06b6d4 !important; background:#ecfeff !important; }\n    .bg-lime{ border-left-color:#16a34a !important; background:#f0fdf4 !important; }\n    .bg-orange{ border-left-color:#f97316 !important; background:#fff7ed !important; }\n    .bg-indigo{ border-left-color:#6366f1 !important; background:#eef2ff !important; }\n    .bg-emerald{ border-left-color:#22c55e !important; background:#ecfdf5 !important; }\n    .bg-slate{ border-left-color:#334155 !important; background:#f8fafc !important; }<\/p>\n<p>    \/* Utilities *\/\n    .tight ul{ margin:0; padding-left:18px; }\n    .tight li{ margin:4px 0; }\n    .mono{ font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace; }\n    .kbd{ background:#e5e7eb; border:1px solid #cbd5e1; padding:1px 6px; border-radius:6px; font-family:ui-monospace,monospace; font-size:.88em; }\n    .muted{ color:#64748b; }\n    .wp-nodejs-pb code{ background:#f1f5f9; padding:0 4px; border-radius:4px; border:1px solid #e2e8f0; }\n    .wp-nodejs-pb pre{\n      background:#f5f5f5; color:#111827; border:1px solid #e5e7eb;\n      padding:12px; border-radius:8px; overflow:auto; font-size:.92rem; line-height:1.55;\n    }\n    .q{font-weight:700;}<\/p>\n<p>    \/* Make long Q&A easier to scan inside a card *\/\n    .qa p{ margin:8px 0; }\n    .qa b{ color:#0f172a; }\n  <\/style>\n<div class=\"wp-nodejs-pb\">\n<div class=\"heading\">\n<h2>Node.js Pocket Book \u2014 Uplatz<\/h2>\n<p>50 deep-dive flashcards \u2022 Wide layout \u2022 Fewer scrolls \u2022 20+ Interview Q&amp;A \u2022 Readable code examples<\/p>\n<\/p><\/div>\n<div class=\"grid\">\n      <!-- ===================== SECTION 1 ===================== --><\/p>\n<div class=\"section-title\">Section 1 \u2014 Fundamentals<\/div>\n<div class=\"card bg-blue\">\n<h3>1) What is Node.js?<\/h3>\n<p>Node.js is a JavaScript runtime built on V8 that runs JS outside the browser. It embraces an event-driven, non-blocking I\/O model so a single process can multiplex thousands of connections, excelling at APIs, real-time features, proxies, and streaming. You get one language across client and server, plus the npm ecosystem. Typical sweet spots: BFF (Backend for Frontend), API gateways, chat\/dashboards, task runners, and CLIs. Less ideal: CPU-bound workloads (video encoding, big crypto) unless you use <code>worker_threads<\/code> or delegate to services. For production, prefer LTS versions and keep dependencies tidy.<\/p>\n<pre><code class=\"mono\"># Check your Node & npm\r\nnode -v\r\nnpm -v<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-green\">\n<h3>2) Why Node.js? Core Strengths &#038; Tradeoffs<\/h3>\n<p>Strengths: speed of delivery, huge package ecosystem, JSON-native APIs, and real-time capabilities with minimal boilerplate. The single-threaded model simplifies concurrency versus managing many threads. Tradeoffs: CPU-heavy work can block the event loop, dependency sprawl requires governance, and callback-based code (legacy) can get messy. Mitigate with <code>async\/await<\/code>, schema validation, and clear architectural boundaries. Node thrives when most time is I\/O (DB, network) rather than CPU.<\/p>\n<pre><code class=\"mono\"># Create a project quickly\r\nnpm init -y\r\nnpm i fastify<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-amber\">\n<h3>3) Event Loop: Mental Model<\/h3>\n<p>The event loop runs phases: <em>timers<\/em> \u2192 pending callbacks \u2192 idle\/prepare \u2192 <em>poll<\/em> \u2192 <em>check<\/em> \u2192 close callbacks. Promise microtasks run between turns and after each callback. Use this to reason about ordering: <code>Promise.then<\/code> fires before <code>setImmediate<\/code>, which fires after <code>poll<\/code>. Practical tip: prefer promises and avoid heavy synchronous work on the main thread.<\/p>\n<pre><code class=\"mono\">setTimeout(() =&gt; console.log('timeout'), 0);\r\nsetImmediate(() =&gt; console.log('immediate'));\r\nPromise.resolve().then(() =&gt; console.log('microtask'));<\/code><\/pre>\n<p class=\"muted\">Typical order: <em>microtask<\/em> \u2192 <em>timeout<\/em>\/<em>immediate<\/em> (depends on scheduling).<\/p>\n<\/p><\/div>\n<div class=\"card bg-violet\">\n<h3>4) libuv &#038; Threadpool<\/h3>\n<p>libuv powers the event loop and a small threadpool (default 4) to offload certain I\/O (file system, DNS, compression, some crypto). You can tune with <code>UV_THREADPOOL_SIZE<\/code> (up to 128), but profile first. Long-running CPU tasks should use <code>worker_threads<\/code>.<\/p>\n<pre><code class=\"mono\">import { createReadStream } from 'node:fs';\r\nimport crypto from 'node:crypto';\r\nconst hash = crypto.createHash('sha256');\r\ncreateReadStream('big.bin').pipe(hash).on('finish', () =&gt; {\r\n  console.log(hash.read().toString('hex'));\r\n});<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-rose\">\n<h3>5) Node vs Browser JS<\/h3>\n<p>Both share ECMAScript, but available APIs differ. Browsers provide DOM, storage, and UI; Node exposes system modules: <code>fs<\/code>, <code>net<\/code>, <code>http<\/code>, <code>cluster<\/code>. Node has no DOM; use libraries (e.g., JSDOM) if you must parse HTML server-side. With Node \u226518, <code>fetch<\/code> is global, narrowing gaps. Security models differ: browser sandbox vs server trust boundary; always validate\/authorize server inputs.<\/p>\n<pre><code class=\"mono\">\/\/ Node \u226518 global fetch\r\nconst res = await fetch('https:\/\/api.example.com');\r\nconst data = await res.json();<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-cyan\">\n<h3>6) npm, pnpm, Yarn<\/h3>\n<p><b>npm<\/b> is default and ubiquitous. <b>pnpm<\/b> uses content-addressable storage; it\u2019s fast and space-efficient for monorepos. Yarn is common in older stacks. Always commit lockfiles for reproducible builds. Helpful scripts:<\/p>\n<pre><code class=\"mono\">\"scripts\": {\r\n  \"dev\": \"node --watch src\/index.js\",\r\n  \"build\": \"tsc -p tsconfig.json\",\r\n  \"test\": \"node --test\",\r\n  \"start\": \"node dist\/index.js\"\r\n}<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-lime\">\n<h3>7) package.json &#038; Exports<\/h3>\n<p>Key fields: <code>type<\/code> (<code>module<\/code> for ESM), <code>main<\/code>\/<code>exports<\/code>, <code>engines<\/code>, <code>scripts<\/code>, <code>dependencies<\/code>. For libraries, the <code>exports<\/code> map controls entry points for ESM\/CJS. Prefer ESM in 2025; publish dual only if consumers need CJS.<\/p>\n<pre><code class=\"mono\">{\r\n  \"type\":\"module\",\r\n  \"exports\": {\r\n    \".\": { \"import\":\".\/dist\/index.mjs\", \"require\":\".\/dist\/index.cjs\" }\r\n  }\r\n}<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-orange\">\n<h3>8) LTS vs Current<\/h3>\n<p>Use LTS in production for stability, security patches, and ecosystem compatibility. Track Current in CI to catch upcoming changes. Pin Node version via <code>.nvmrc<\/code> or container images and enforce with <code>engines<\/code>.<\/p>\n<pre><code class=\"mono\"># Pin in project root\r\necho \"lts\/*\" &gt; .nvmrc<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-indigo\">\n<h3>9) nvm &#038; Multi-Version Dev<\/h3>\n<p>Install multiple Node versions and switch per project; align with <code>\"engines\"<\/code>. Team tip: add <code>.nvmrc<\/code> and document setup. CI should mirror the specified version.<\/p>\n<pre><code class=\"mono\">nvm install --lts\r\nnvm use --lts<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-emerald\">\n<h3>10) Q&#038;A \u2014 \u201cHow is Node concurrent if it\u2019s single-threaded?\u201d<\/h3>\n<p><span class=\"q\">Answer:<\/span> JavaScript runs on one thread, but I\/O is asynchronous. The event loop and libuv handle non-blocking operations; many requests can wait on I\/O simultaneously. When I\/O completes, callbacks\/microtasks are queued. The result is high concurrency without thread-per-request overhead. For CPU-heavy tasks, use <code>worker_threads<\/code> or separate services so the loop stays responsive.<\/p>\n<\/p><\/div>\n<p>      <!-- ===================== SECTION 2 ===================== --><\/p>\n<div class=\"section-title\">Section 2 \u2014 Core APIs &#038; Modules<\/div>\n<div class=\"card bg-blue\">\n<h3>11) Modules: ESM vs CJS<\/h3>\n<p>ESM (<code>import\/export<\/code>) is the modern standard; CJS (<code>require\/module.exports<\/code>) remains in legacy code. ESM has strict file extensions\/resolution and top-level <code>await<\/code>. For Node apps, set <code>\"type\":\"module\"<\/code> and convert gradually. For interop, use dynamic <code>import()<\/code> from CJS, or <code>createRequire<\/code> from ESM.<\/p>\n<pre><code class=\"mono\">\/\/ esm.mjs\r\nimport os from 'node:os';\r\nexport const platform = os.platform();<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-green\">\n<h3>12) fs &#038; path Essentials<\/h3>\n<p>Prefer promise APIs and streaming for large files. Always handle ENOENT\/permissions and avoid sync calls in servers.<\/p>\n<pre><code class=\"mono\">import { readFile, writeFile } from 'node:fs\/promises';\r\nimport { join } from 'node:path';\r\nconst p = join(process.cwd(),'data.json');\r\nawait writeFile(p, JSON.stringify({ok:true}));\r\nconst raw = await readFile(p,'utf8');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-amber\">\n<h3>13) HTTP\/HTTPS Servers<\/h3>\n<p>Low-level servers give full control but require boilerplate (parsing, routing). In production, frameworks improve productivity, validation, and error handling. Always set sensible timeouts.<\/p>\n<pre><code class=\"mono\">import http from 'node:http';\r\nconst s = http.createServer((req,res) =&gt; {\r\n  res.setHeader('content-type','application\/json');\r\n  res.end(JSON.stringify({ path:req.url }));\r\n});\r\ns.listen(3000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-violet\">\n<h3>14) Streams &#038; Backpressure<\/h3>\n<p>Streams process data incrementally, reducing memory pressure. Use <code>stream\/promises.pipeline<\/code> to connect safely and respect backpressure.<\/p>\n<pre><code class=\"mono\">import { pipeline } from 'node:stream\/promises';\r\nimport { createReadStream, createWriteStream } from 'node:fs';\r\nawait pipeline(createReadStream('in.bin'), createWriteStream('out.bin'));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-rose\">\n<h3>15) Buffer &#038; Binary Data<\/h3>\n<p><code>Buffer<\/code> represents raw bytes. Be mindful of encodings and size. Avoid constructing huge buffers; stream instead.<\/p>\n<pre><code class=\"mono\">const b = Buffer.from('hello','utf8');\r\nconsole.log(b.toString('hex'));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-cyan\">\n<h3>16) Crypto Basics<\/h3>\n<p>Use modern algorithms and safe defaults; for passwords, use bcrypt\/argon2 (not plain hashes). Prefer AEAD modes (AES-GCM) for encryption. Don\u2019t roll your own crypto.<\/p>\n<pre><code class=\"mono\">import crypto from 'node:crypto';\r\nconst hash = crypto.createHash('sha256').update('data').digest('hex');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-lime\">\n<h3>17) Events &#038; EventEmitter<\/h3>\n<p>Emitters enable decoupled modules. Clean up listeners, handle <code>'error'<\/code>, and avoid memory leaks.<\/p>\n<pre><code class=\"mono\">import { EventEmitter } from 'node:events';\r\nconst bus = new EventEmitter();\r\nbus.on('tick', (n) =&gt; console.log('tick', n));\r\nsetInterval(() =&gt; bus.emit('tick', Date.now()), 1000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-orange\">\n<h3>18) Timers &#038; Scheduling<\/h3>\n<p><code>setTimeout<\/code>, <code>setInterval<\/code>, <code>setImmediate<\/code> schedule work; clear on shutdown. For cron-like tasks, use external schedulers or job queues.<\/p>\n<pre><code class=\"mono\">const id = setInterval(() =&gt; console.log('beat'), 1000);\r\nsetTimeout(() =&gt; clearInterval(id), 5000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-indigo\">\n<h3>19) process &#038; Env Config<\/h3>\n<p>Validate env at startup (zod\/joi). Handle signals for graceful shutdown. Catch unhandled rejections\/exceptions to log, then exit (don\u2019t continue in a corrupted state).<\/p>\n<pre><code class=\"mono\">process.on('SIGTERM', () =&gt; { \/* stop accepting, drain, exit *\/ });\r\nprocess.on('unhandledRejection', (e) =&gt; { console.error(e); process.exit(1); });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-emerald\">\n<h3>20) Q&#038;A \u2014 \u201cESM vs CJS: what should I choose?\u201d<\/h3>\n<p><span class=\"q\">Answer:<\/span> Prefer ESM for new apps\/packages; it\u2019s standard, supports top-level <code>await<\/code>, and aligns with browsers. If consumers need CJS, publish dual exports via <code>exports<\/code> map. Avoid runtime module-format hacks; keep builds simple. Use dynamic <code>import()<\/code> or <code>createRequire<\/code> for interop.<\/p>\n<\/p><\/div>\n<p>      <!-- ===================== SECTION 3 ===================== --><\/p>\n<div class=\"section-title\">Section 3 \u2014 Async, Patterns &#038; Concurrency<\/div>\n<div class=\"card bg-blue\">\n<h3>21) From Callbacks to Promises<\/h3>\n<p>Legacy Node used error-first callbacks (<code>(err, data) =&gt; {}<\/code>). Modern code should adopt promises and <code>async\/await<\/code> for readability and error handling. Convert with <code>util.promisify<\/code> when needed. Ensure all async paths are awaited to avoid \u201cfloating\u201d promises and unhandled rejections.<\/p>\n<pre><code class=\"mono\">import { promisify } from 'node:util';\r\nimport { readFile } from 'node:fs';\r\nconst read = promisify(readFile);\r\nconst txt = await read('file.txt','utf8');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-green\">\n<h3>22) async\/await Best Practices<\/h3>\n<p>Group related awaits in a single <code>try\/catch<\/code>, fail fast with explicit messages, and use <code>Promise.all<\/code> for independent tasks. For best-effort tasks, use <code>allSettled<\/code>.<\/p>\n<pre><code class=\"mono\">const [user, orders] = await Promise.all([getUser(id), listOrders(id)]);\r\nif (!user) throw new Error('User not found');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-amber\">\n<h3>23) Microtasks vs Macrotasks<\/h3>\n<p>Promises\/microtasks run before the next event loop phase. Timers\/IO callbacks are macrotasks. Ordering matters for tests and subtle race conditions.<\/p>\n<pre><code class=\"mono\">queueMicrotask(() =&gt; console.log('microtask'));\r\nsetImmediate(() =&gt; console.log('immediate'));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-violet\">\n<h3>24) nextTick vs queueMicrotask<\/h3>\n<p><code>process.nextTick<\/code> runs before the microtask queue and can starve I\/O if abused; <code>queueMicrotask<\/code> follows standard microtask semantics and is safer for most cases. Prefer <code>queueMicrotask<\/code> in libs to avoid priority surprises.<\/p>\n<pre><code class=\"mono\">process.nextTick(() =&gt; {\/* use sparingly *\/});\r\nqueueMicrotask(() =&gt; {\/* preferred microtask *\/});<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-rose\">\n<h3>25) Worker Threads<\/h3>\n<p>Use workers for CPU-bound tasks (image resize, compression, crypto, ML inference). Communicate via <code>parentPort.postMessage<\/code> or <code>MessageChannel<\/code>. Keep messages small or share memory via <code>SharedArrayBuffer<\/code>. Pool workers for throughput.<\/p>\n<pre><code class=\"mono\">import { Worker } from 'node:worker_threads';\r\nconst w = new Worker(new URL('.\/heavy.js', import.meta.url));\r\nw.postMessage({ payload: 'data' });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-cyan\">\n<h3>26) Cluster &#038; Multi-Process<\/h3>\n<p><code>cluster<\/code> forks workers to utilize multi-core CPUs. Good for HTTP servers; combine with PM2\/systemd. Consider sticky sessions for WebSockets. In containers, prefer one worker per container and scale horizontally via orchestrator.<\/p>\n<pre><code class=\"mono\">import cluster from 'node:cluster';\r\nimport os from 'node:os';\r\nif (cluster.isPrimary) os.cpus().forEach(() =&gt; cluster.fork());\r\nelse server.listen(3000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-lime\">\n<h3>27) Streams: Backpressure in Practice<\/h3>\n<p>When <code>write()<\/code> returns false, pause reads until <code>'drain'<\/code>. Using <code>pipeline<\/code> handles this automatically. Backpressure prevents memory spikes and smooths throughput under load.<\/p>\n<pre><code class=\"mono\">const ok = writable.write(chunk);\r\nif (!ok) readable.pause();\r\nwritable.once('drain', () =&gt; readable.resume());<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-orange\">\n<h3>28) Queues, Jobs &#038; Rate Limits<\/h3>\n<p>Offload slow\/retryable tasks via BullMQ\/RabbitMQ\/Kafka. Implement exponential backoff with jitter, dead-letter queues, and idempotency keys. Job queues decouple latency from request handling.<\/p>\n<pre><code class=\"mono\">import { Queue } from 'bullmq';\r\nconst q = new Queue('emails',{ connection:{ host:'127.0.0.1', port:6379 }});\r\nawait q.add('welcome',{ userId:'u1' });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-indigo\">\n<h3>29) Timeouts, Retries &#038; Circuit Breakers<\/h3>\n<p>Set outbound call timeouts by default, retry carefully (idempotent ops), and trip a circuit breaker on sustained failures. Expose breaker state for ops and dashboards.<\/p>\n<pre><code class=\"mono\">const controller = new AbortController();\r\nsetTimeout(() =&gt; controller.abort(), 2000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-emerald\">\n<h3>30) Q&#038;A \u2014 \u201cWhen should I use workers vs cluster?\u201d<\/h3>\n<p><span class=\"q\">Answer:<\/span> Use <b>workers<\/b> for CPU-bound tasks within a single process to avoid blocking the loop. Use <b>cluster<\/b> to scale an HTTP server across cores (multi-process). They complement each other: a clustered web server can dispatch CPU-heavy jobs to a worker pool, keeping request latency low.<\/p>\n<\/p><\/div>\n<p>      <!-- ===================== SECTION 4 ===================== --><\/p>\n<div class=\"section-title\">Section 4 \u2014 Frameworks, Data &#038; APIs<\/div>\n<div class=\"card bg-blue\">\n<h3>31) Express<\/h3>\n<p>Minimalist and battle-tested. Great ecosystem of middleware. Establish conventions for error handling, validation, and async functions (wrap with error middleware).<\/p>\n<pre><code class=\"mono\">import express from 'express';\r\nconst app = express();\r\napp.use(express.json());\r\napp.get('\/health', (_req,res) =&gt; res.json({ ok:true }));\r\napp.listen(3000);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-green\">\n<h3>32) Fastify<\/h3>\n<p>Schema-first, high throughput, and excellent plugin system. Built-in AJV validation speeds safe APIs and generates OpenAPI. If performance and correctness matter, Fastify is a strong default.<\/p>\n<pre><code class=\"mono\">import Fastify from 'fastify';\r\nconst f = Fastify();\r\nf.get('\/health', async () =&gt; ({ ok:true }));\r\nawait f.listen({ port:3000 });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-amber\">\n<h3>33) NestJS<\/h3>\n<p>Opinionated framework with modules, providers, controllers, and DI \u2014 great for large teams. Encourages SOLID principles, testability, and separation of concerns.<\/p>\n<pre><code class=\"mono\">\/\/ Nest CLI\r\nnpx @nestjs\/cli new app<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-violet\">\n<h3>34) REST Design<\/h3>\n<p>Use nouns, proper status codes, pagination, filtering, idempotency keys, and versioning. Document with OpenAPI and keep examples current. Enforce input\/output schemas.<\/p>\n<pre><code class=\"mono\">\/\/ Fastify schema on route\r\nf.post('\/users', {\r\n  schema:{ body:{ type:'object', required:['email'], properties:{ email:{ type:'string', format:'email'} } }\r\n}}, async (req) =&gt; ({ id:'u_123', email:req.body.email }));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-rose\">\n<h3>35) GraphQL<\/h3>\n<p>Typed schema, single endpoint, client-driven queries. Control complexity\/depth; batch N+1 with <code>dataloader<\/code>. Map auth to your domain rules; consider persisted queries for caching\/CDN.<\/p>\n<pre><code class=\"mono\">const typeDefs = `type Query { hello: String }`;\r\nconst resolvers = { Query:{ hello: () =&gt; 'world' } };<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-cyan\">\n<h3>36) WebSockets &#038; Real-Time<\/h3>\n<p>Use <code>ws<\/code> or Socket.IO for chat, presence, live dashboards. Plan authentication and reconnection strategies. Horizontal scaling may need sticky sessions or pub\/sub (Redis, NATS).<\/p>\n<pre><code class=\"mono\">import { WebSocketServer } from 'ws';\r\nconst wss = new WebSocketServer({ port:8080 });\r\nwss.on('connection', ws =&gt; ws.send('hello'));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-lime\">\n<h3>37) SQL: Prisma \/ Knex \/ TypeORM<\/h3>\n<p>Prisma offers type-safe client and migrations; Knex is a flexible query builder; TypeORM provides decorators and patterns. Always parameterize queries and index hot paths.<\/p>\n<pre><code class=\"mono\">\/\/ Prisma schema snippet\r\nmodel User { id String @id @default(cuid()) email String @unique createdAt DateTime @default(now()) }<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-orange\">\n<h3>38) NoSQL: MongoDB \/ Redis<\/h3>\n<p>Model read\/write patterns; avoid unbounded documents. MongoDB with Mongoose adds schemas\/validation; Redis excels at caching, queues, and rate limits. Use TTL keys and avoid hot keys where possible.<\/p>\n<pre><code class=\"mono\">import { createClient } from 'redis';\r\nconst r = createClient({ url: process.env.REDIS_URL });\r\nawait r.connect();\r\nawait r.set('health','ok',{ EX:60 });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-indigo\">\n<h3>39) Caching Strategy<\/h3>\n<p>Layer caches: in-process (LRU), Redis, and HTTP (CDN). Use ETags\/Last-Modified, cache keys with versioning, and request coalescing to prevent stampedes. Invalidate carefully on writes.<\/p>\n<pre><code class=\"mono\">\/\/ Example HTTP cache headers\r\nres.setHeader('Cache-Control','public, max-age=60');\r\nres.setHeader('ETag', etag);<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-emerald\">\n<h3>40) Q&#038;A \u2014 \u201cREST vs GraphQL in Node?\u201d<\/h3>\n<p><span class=\"q\">Answer:<\/span> REST is simpler, cache-friendly, and great for standard CRUD and integrations. GraphQL shines when clients need flexible shapes and multiple resources in one round-trip. In Node, Express\/Fastify make REST trivial; Apollo\/Nest make GraphQL ergonomic. Choose REST for broad compatibility; GraphQL for complex, client-driven UIs. You can mix: REST for public APIs, GraphQL for internal apps.<\/p>\n<\/p><\/div>\n<p>      <!-- ===================== SECTION 5 ===================== --><\/p>\n<div class=\"section-title\">Section 5 \u2014 Security, Testing, Deployment, Observability &#038; Interview Q&#038;A<\/div>\n<div class=\"card bg-blue\">\n<h3>41) Security Fundamentals<\/h3>\n<p>Validate inputs (AJV\/zod), sanitize outputs, enforce HTTPS, set security headers (helmet), rotate secrets, and restrict privileges. Regularly audit dependencies. Log authz decisions and deny by default. Never trust client-supplied IDs without authorization checks.<\/p>\n<pre><code class=\"mono\">\/\/ Example with dotenv + validation\r\nimport 'dotenv\/config';\r\nif(!process.env.DB_URL) throw new Error('DB_URL required');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-green\">\n<h3>42) Auth &#038; Sessions<\/h3>\n<p>Stateless APIs: short-lived JWT with rotation\/blacklist on logout. Stateful apps: signed cookies backed by server store. For OAuth\/OIDC, leverage libraries and validate nonce\/state. Always bind sessions to device context and rotate tokens on privilege changes.<\/p>\n<pre><code class=\"mono\">\/\/ Pseudocode: Verify JWT\r\nconst payload = verify(token, PUBLIC_KEY, { algorithms:['RS256'] });<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-amber\">\n<h3>43) Testing Strategy<\/h3>\n<p>Use built-in <code>node:test<\/code> or Jest. Combine unit, integration, and contract tests. For HTTP, pair with <code>supertest<\/code>. Mock external services sparingly; prefer ephemeral test DBs with seed data. Run coverage in CI.<\/p>\n<pre><code class=\"mono\">import test from 'node:test';\r\nimport assert from 'node:assert\/strict';\r\ntest('adds', () =&gt; assert.equal(2+2,4));<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-violet\">\n<h3>44) Linting, Formatting &#038; Types<\/h3>\n<p>ESLint + Prettier keep style consistent; TypeScript catches bugs. Enforce strict TS options, define interfaces for domain models, and use <code>tsc --noEmit<\/code> in CI to ensure type safety even in JS projects via JSDoc types.<\/p>\n<pre><code class=\"mono\">pnpm add -D eslint prettier typescript @types\/node<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-rose\">\n<h3>45) Performance &#038; Profiling<\/h3>\n<p>Measure, don\u2019t guess. Use <code>--inspect<\/code> with DevTools, flamegraphs (Clinic), and custom timers. Fix hot paths: avoid sync APIs, batch I\/O, enable HTTP keep-alive, compress wisely, and prefer Fastify if you need throughput.<\/p>\n<pre><code class=\"mono\">node --inspect server.js\r\n\/\/ Open chrome:\/\/inspect<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-cyan\">\n<h3>46) Deployment Options<\/h3>\n<p>PM2 for simple VMs; Docker for portability; Kubernetes for orchestration and autoscaling; serverless (Lambda\/Cloud Functions) for spiky workloads. Implement health\/readiness, graceful shutdown, and env-specific configs. Keep images slim and pin Node versions.<\/p>\n<pre><code class=\"mono\">FROM node:18-alpine\r\nWORKDIR \/app\r\nCOPY package*.json .\/\r\nRUN npm ci --omit=dev\r\nCOPY . .\r\nCMD [\"node\",\"dist\/index.js\"]<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-lime\">\n<h3>47) Observability<\/h3>\n<p>Structured logs (pino) with request IDs, metrics (Prometheus) for latency\/RPS\/error rate, and tracing (OpenTelemetry) across services. Build SLOs (e.g., p99 latency &lt; 300ms) and alert on burn rates. Expose <code>\/health<\/code> and <code>\/ready<\/code> endpoints.<\/p>\n<pre><code class=\"mono\">import pino from 'pino';\r\nconst log = pino({ level: process.env.LOG_LEVEL || 'info' });\r\nlog.info({ event:'startup' }, 'service online');<\/code><\/pre>\n<\/p><\/div>\n<div class=\"card bg-orange tight\">\n<h3>48) Prod Checklist<\/h3>\n<ul>\n<li>Env validation &#038; secrets manager<\/li>\n<li>Timeouts, retries, circuit breakers<\/li>\n<li>Input validation, rate limits, headers<\/li>\n<li>Graceful shutdown &#038; draining<\/li>\n<li>Dashboards: latency, errors, saturation<\/li>\n<li>Runbooks &#038; on-call escalation<\/li>\n<\/ul><\/div>\n<div class=\"card bg-indigo\">\n<h3>49) Common Pitfalls<\/h3>\n<p>Blocking the loop with CPU or sync <code>fs<\/code>, unhandled promise rejections, leaking event listeners\/streams, mixing CJS\/ESM incorrectly, missing timeouts, and non-idempotent retries. Prevent with lint rules, tests, observability, and architectural guardrails (queues, backpressure, bounded caches).<\/p>\n<\/p><\/div>\n<div class=\"card bg-emerald qa\">\n<h3>50) Interview Q&amp;A \u2014 20 Practical Questions (Expanded)<\/h3>\n<p><b>1) Why Node for APIs?<\/b> Non-blocking I\/O, JSON-native data flow, and huge ecosystem enable rapid delivery. Great for I\/O-bound workloads and microservices.<\/p>\n<p><b>2) Single-threaded yet concurrent?<\/b> Event loop multiplexes I\/O. libuv handles OS operations; callbacks run when ready. Use workers\/cluster for CPU and scale-out.<\/p>\n<p><b>3) ESM vs CJS?<\/b> Prefer ESM; publish dual exports if consumers require CJS. Avoid mixing without a plan; use <code>exports<\/code> map.<\/p>\n<p><b>4) Avoiding callback hell?<\/b> Adopt promises and <code>async\/await<\/code>, modularize functions, centralize error handling, and maintain clear control flow.<\/p>\n<p><b>5) nextTick vs queueMicrotask?<\/b> <code>nextTick<\/code> runs before other microtasks and can starve I\/O; <code>queueMicrotask<\/code> follows standard semantics \u2014 safer for libraries.<\/p>\n<p><b>6) Preventing memory leaks?<\/b> End streams, clear timers, remove listeners, bound caches, and use heap snapshots\/metrics to detect growth early.<\/p>\n<p><b>7) Backpressure handling?<\/b> Use <code>pipeline<\/code>, respect <code>write()<\/code> return values, and pause\/resume streams to match producer\/consumer speeds.<\/p>\n<p><b>8) Secure configuration?<\/b> Validate env on boot, store secrets in a manager, rotate keys, and restrict permissions (least privilege).<\/p>\n<p><b>9) Rate limiting strategy?<\/b> Sliding window counters in Redis keyed by IP\/user\/route; return 429s and include <code>Retry-After<\/code>.<\/p>\n<p><b>10) Auth choices?<\/b> JWT for stateless APIs (short TTL + rotation); cookies + server store for web sessions. Protect refresh flows and use HTTPS only.<\/p>\n<p><b>11) GraphQL hardening?<\/b> Complexity\/depth limits, persisted queries, input validation, and dataloaders to avoid N+1.<\/p>\n<p><b>12) When to use workers?<\/b> CPU-heavy tasks (image, PDF, crypto, ML). Keep messages small; consider SharedArrayBuffer for large data.<\/p>\n<p><b>13) Cluster vs Kubernetes scaling?<\/b> Cluster uses all cores on one host; Kubernetes scales containers across nodes with health checks and autoscaling.<\/p>\n<p><b>14) Safe retries?<\/b> Retry only idempotent operations, add jitter\/backoff, and use idempotency keys + DLQs to prevent duplicates.<\/p>\n<p><b>15) Observability must-haves?<\/b> Correlated request IDs, structured logs, metrics (latency histograms, RPS, errors), and distributed tracing.<\/p>\n<p><b>16) DB performance tips?<\/b> Use pools, prepared statements, proper indexes, pagination, and cache hot reads. Monitor slow queries.<\/p>\n<p><b>17) DoS protections?<\/b> Timeouts, body size limits, schema validation, WAF\/CDN, circuit breakers, and rate limits per user\/route.<\/p>\n<p><b>18) Graceful shutdown?<\/b> Stop accepting new requests, drain connections\/queues, close DB pools, flush logs, then exit with code 0.<\/p>\n<p><b>19) Testing pyramid?<\/b> Emphasize unit, add integration for boundaries, and selective e2e. Use contract tests for inter-service APIs.<\/p>\n<p><b>20) Framework choice?<\/b> Express for minimalism, Fastify for performance\/schema, Nest for large teams seeking opinionated structure.<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Node.js Pocket Book \u2014 Uplatz 50 deep-dive flashcards \u2022 Wide layout \u2022 Fewer scrolls \u2022 20+ Interview Q&amp;A \u2022 Readable code examples Section 1 \u2014 Fundamentals 1) What is Node.js? <span class=\"readmore\"><a href=\"https:\/\/uplatz.com\/blog\/node-js-pocket-book\/\">Read More &#8230;<\/a><\/span><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2461,2462],"tags":[],"class_list":["post-4398","post","type-post","status-publish","format-standard","hentry","category-node-js","category-pocket-book"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Node.js Pocket Book | Uplatz Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/uplatz.com\/blog\/node-js-pocket-book\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Node.js Pocket Book | Uplatz Blog\" \/>\n<meta property=\"og:description\" content=\"Node.js Pocket Book \u2014 Uplatz 50 deep-dive flashcards \u2022 Wide layout \u2022 Fewer scrolls \u2022 20+ Interview Q&amp;A \u2022 Readable code examples Section 1 \u2014 Fundamentals 1) What is Node.js? 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