V8 is Google's open-source JavaScript engine, written in C++, and Node.js embeds it to run JavaScript outside the browser. V8 compiles your code to bytecode, a compact instruction format that its Ignition interpreter runs. While the code runs, V8 tracks the types it sees and the shapes of objects, which it calls hidden classes. Its just-in-time (JIT) compilers then turn functions that run often into optimized machine code.
V8 also manages the heap and garbage collection, but it does no I/O itself. Node.js handles I/O through libuv, a separate C library it bundles for the event loop and the thread pool.
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