What is the difference between closure-based data hiding and #private fields 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.
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More FAQs in Closures: Data Hiding and Encapsulation 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.
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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