## Single-Threaded Non-Blocking Concurrency JavaScript is single-threaded: it has exactly **one Call Stack** and executes one statement at a time. Yet, web applications handle thousands of concurrent network requests, UI clicks, and animations seamlessly. This magic is powered by the **Event Loop** operating in coordination with browser Web APIs / Node.js libuv: ```text [ Synchronous Call Stack ] ────▶ (Runs statements to completion) │ ▼ (Stack Empty) [ Microtask Queue ] ───────────▶ (Promise.then, queueMicrotask, MutationObserver) │ * Drained COMPLETELY before moving on! ▼ [ Animation Frame Queue ] ─────▶ (requestAnimationFrame, UI Layout Repaint) │ ▼ [ Macrotask Queue (Task) ] ────▶ (setTimeout, setInterval, I/O, setImmediate) * Executes ONE single macrotask per tick! ```