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.