Which is more memory-efficient for data privacy in JavaScript, closures or #private fields?
#private fields. Methods are on the prototype (shared across instances), so memory is lower. Closure-based methods are per-instance (each instance gets its own copy), which uses more memory for many instances.
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More FAQs in Closures vs Classes for Data Privacy in JavaScript
Closures use a function's lexical environment for privacy (per-instance methods, no this, functional style). #private fields use the # syntax on class instances (shared prototype methods, this-based, class-based with inheritance).
For functional style (prefering functions over classes), to avoid this binding issues (arrow methods), for simple factories with few instances, or in older environments that do not support ES2022 #private fields.
Yes. You can use #private fields for state and arrow methods (per-instance) that close over this. This avoids this binding issues but costs memory (per-instance methods). Use sparingly, only when this binding is a real problem.
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