NodeJS

Unhandled promise rejections in Node.js cause intermittent crashes and must be caught globally. You can attach rejection handlers to manage async errors, prevent process termination, and maintain server stability during backend execution.

The Node.js event loop blocks because fs.readFileSync executes synchronous disk I/O on the main thread. This prevents concurrent async operations, degrading backend performance. Using asynchronous fs methods ensures continuous event loop responsiveness.

The __dirname variable is undefined in Node.js ESM modules because it is a CommonJS-specific global. You can construct an equivalent path using import.meta.url and the fileURLToPath API to navigate directories within an ESM environment.

Memory leaks in Node.js occur when event listeners accumulate without removal, retaining objects in memory indefinitely. Continuously adding listeners to emitters without calling removeListener bloats memory usage and degrades backend application performance.

CommonJS uses require and module.exports for synchronous module loading, while ESM uses import and export for asynchronous module handling. Node.js supports both, but mixing them requires understanding specific interoperability rules.

Preventing event loop blocking in Node.js requires offloading heavy computations and utilizing asynchronous APIs. Avoiding synchronous operations like readFileSync ensures the event loop remains free to handle concurrent backend requests efficiently.