V8 Engine Optimization: Hidden Classes and Inline Caching

V8 optimizes JS by creating 'Hidden Classes' for objects and using 'Inline Caches' to speed up property access based on previous lookups.

JavaScript is dynamic, but V8 creates static 'Hidden Classes' (Shapes) under the hood. When you add a property to an object, V8 transitions to a new Hidden Class. If two objects share the same properties in the same order, they share a Hidden Class. Inline Caching (IC) remembers the memory offset of a property for a specific Hidden Class. If you pass objects with different shapes to the same function, V8 becomes 'polymorphic' or 'megamorphic', breaking IC and slowing down execution significantly.