Hidden Classes

Hidden classes are a way that JavaScript engines optimize how objects are stored in memory. Think of objects as collections of properties (key-value pairs). When similar objects are created, the engine groups them into "hidden classes"—internal templates that describe their structure and property order. This allows the engine to access and modify properties more efficiently, akin to using a blueprint. As objects change, the engine updates their hidden classes to maintain optimized performance. Hidden classes are an internal implementation detail that helps JavaScript run faster, but they are not visible to programmers.