Node.js callbacks follow an error-first pattern, where `err` is always the first argument, representing success or errors in asynchronous operations. Understanding this pattern is crucial for building scalable applications.
The article demystifies JavaScript’s event loop—its call stack and task queue—and how a single-threaded engine achieves concurrency by scheduling callbacks, promises, and async/await to handle I/O like AJAX and timers without blocking. It offers best practices (avoid blocking, use Web APIs/workers), a simple XHR example, and a chat-app use case to keep UIs responsive, scalable, and real-time.
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