The engine that turns your JavaScript into a running program — parsing, compiling, and cleaning up after it.
V8 is the engine behind Chrome and Node.js, and it doesn't just execute JavaScript — it manages a whole pipeline to get there. Your code first becomes an AST, then Ignition (V8's interpreter) turns that into bytecode and starts running it immediately, so there's no long compile step before anything happens. While Ignition runs, V8 watches for functions worth optimizing and sends them to TurboFan, the optimizing compiler, which is where the JIT behavior lives.
The other half of V8's job is memory. Every object you create lives on the heap, which V8 splits into a small young generation (for short-lived objects, collected fast and often) and a larger old generation (for objects that survive, collected less often but more thoroughly). Garbage collection here isn't one algorithm — V8 uses a fast copying collector (Scavenger) for young objects and a mark-sweep-compact collector for old ones, much of it running incrementally or concurrently so it doesn't freeze your program.
What you'll walk away knowing