Node.js — Runtime Internals, Express, APIs and SQL Server Cheat Sheet

Node.js — Runtime Internals, Express, APIs and SQL Server

What Node.js is and how it works inside (V8, libuv, the event loop phases, thread pool, non-blocking I/O), modules (CommonJS vs ES modules), npm and package.json, the core modules (fs, path, http, events, streams, buffer), asynchronous patterns (callbacks, promises, async/await), Express.js REST APIs with middleware and error handling, project folder structure, connecting to SQL Server (mssql, Prisma, Sequelize), authentication with JWT, worker threads and clustering, testing, security, performance, deployment and the Node.js interview questions.

Architecture

V8 (JS engine) + libuv (event loop, thread pool of 4, async I/O) · your JS on one main thread · I/O non-blocking · CPU work → worker threads.

Event loop order

sync code → process.nextTick → promise microtasks → timers → pending → poll (I/O) → check (setImmediate) → close callbacks.

Express essentials

express.json() · routers per feature · middleware order matters · (err, req, res, next) error handler · Express 5 async errors · helmet, cors, rate limit, validation.

SQL Server from Node

mssql ConnectionPool once · .input(name, type, value) parameters · .execute(proc) · sql.Transaction · encrypt: true (Azure) · Prisma provider = "sqlserver" · secrets in env vars.

Production

LTS (even) versions · npm ci · NODE_ENV=production · PM2/cluster or containers · graceful SIGTERM shutdown · pino logging · monitor event-loop lag and heap.