How V8 turns your code into speed — and where it quietly breaks.
JavaScript doesn run the way you write it. Engines like V8 first interpret your code line by line to get things going fast, then watch for functions that run over and over — the 'hot' paths — and hand those off to a Just-In-Time (JIT) compiler that turns them into optimized machine code while your program is still running.
That optimization is optimistic: the engine guesses about the shapes and types your code will keep using, and speeds things up accordingly. When a guess turns out wrong, it throws away the fast version and falls back to slower code — a deoptimization. Most real-world JS performance problems trace back to accidentally triggering exactly that.
What you'll walk away knowing