Why are prototype methods more memory-efficient than closure-based methods in JavaScript?
Because prototype methods are shared across all instances (one copy). Methods created inside the constructor (on this) are per-instance (one copy per instance). For many instances, the memory difference is significant.
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More FAQs in Function Constructors and Closures in JavaScript
By declaring variables with let or var inside the constructor and creating methods on this that close over them. The variables are in the constructor's local scope and are not accessible as properties, only through the methods.
Methods created inside the constructor (on this) are per-instance, not shared on the prototype. Each instance gets its own copy, which uses more memory than prototype methods. ES6 classes with #private fields solve this.
ES6 classes with #private fields (ES2022). They provide true privacy without the memory cost of per-instance methods. Private fields are not accessible outside the class, and methods are shared on the prototype.
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