Bits of .NET

Private class fields with # work but WeakMap provides better encapsulation and no memory leaks.

Private Fields Approach:

class Counter {
    #count = 0;  // Private
    
    increment() { this.#count++; }
    get value() { return this.#count; }
}

WeakMap Approach:

const _private = new WeakMap();

class Counter {
    constructor() {
        _private.set(this, { count: 0, history: [] });
    }
    
    increment() {
        const data = _private.get(this);
        data.history.push(data.count);
        data.count++;
    }
    
    get value() {
        return _private.get(this).count;
    }
    
    get history() {
        return [..._private.get(this).history];
    }
}

const c = new Counter();
c.increment();
console.log(c.value);  // 1
// c._private undefined - truly private!

Memory Advantage: When Counter instance is garbage collected, WeakMap entry automatically removed!