JavaScript FinalizationRegistry & WeakRefs.

finalization-registry.js

const $REF = Symbol();
const $DEL = Symbol();

/**
 * Set a cleanup callback for the specified object.
 * @param {object} target
 * The target value to register.
 * @param {Function} callback
 * Function called when the target is garbage-collected.
 * @returns {Function}
 * A function to unregister the target value.
 */
function ongc(target, callback) {
    const token = {};
    let timer = null;

    const reg = new FinalizationRegistry(
        () => callback(clearInterval(timer))
    );
  
    reg.register(target, undefined, token);
    timer = setInterval(() => reg, 2_147_483_647);
  
    return () => {
        clearInterval(timer);
        reg.unregister(token);
    };
}

class WeakRefs {
    #set = new Set();

    has(item) {
        return this.#set.has(item[$REF]?.deref?.());
    }

    add(item) {
        const ref = new WeakRef(item);
        item[$REF] = new WeakRef(ref);
        item[$DEL] = ongc(item, () => this.#set.delete(ref));
        this.#set.add(ref);
    }

    delete(item) {
        item[$DEL]?.();
        return this.#set.delete(item[$REF]?.deref?.());
    }

    *[Symbol.iterator]() {
        for (let ref of this.#set)
            if (ref = ref.deref())
                yield ref;
    }
}

Reserved.