How does V8 optimize JavaScript code?

Internal labels assigned to objects based on their shape (property names and order). Objects with the same hidden class share optimized code. Different shapes create new hidden classes, causing deoptimization and slower code.

V8 caches the memory location of a property accessed in a hot function. Next time, it directly reads from the cached location (fast). If the hidden class changes, the cache is invalidated and the function deoptimizes.

Passing objects with different hidden classes, adding properties after construction, deleting properties, changing argument types, and using eval, with, or delete. Deoptimization discards optimized machine code and falls back to bytecode.