JavaScript Internals

JavaScript Internals is the foundation of every SDE-2 frontend interview — if you understand the runtime, event loop, and memory model, async bugs, performance issues, and polyfill questions become predictable.

This module walks through the full runtime environment with step-by-step examples: call stack traces, microtask vs macrotask ordering, debounce/throttle internals, V8 optimization, GC, and Web Workers.

Mastering this module means you can predict async output in whiteboard questions, explain why the UI freezes during heavy synchronous work, and describe how the browser keeps I/O non-blocking despite JavaScript being single-threaded.

Covers the runtime vs engine split, call stack overflow, microtask priority over macrotasks, Promises and async/await ordering, closure memory, V8 hidden classes, mark-and-sweep GC, and moving heavy work off-thread with Web Workers.