How do closures provide data hiding in JavaScript?
By declaring variables inside a function's lexical environment and returning methods that access them. The variables are not accessible directly from outside, only through the returned methods. This is encapsulation.
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More FAQs in Closures: Data Hiding and Encapsulation in JavaScript
Closure variables are in the function's lexical environment (per-instance methods, functional style, no this). #private fields are on the class instance (methods shared on prototype, more memory-efficient, class-based). Both achieve true privacy.
True privacy (variables are completely inaccessible), no this issues (methods are often arrows), functional style (works without classes), and per-instance state (each factory call creates a separate private scope).
Memory (each instance gets its own copy of the methods, not shared on a prototype), harder to test (private state is not directly inspectable), and no inheritance (closures do not support class-based inheritance patterns).
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