FinalizationRegistry

FinalizationRegistry.js

// by @noseratio
// see https://v8.dev/features/weak-references

class Transient {
  static #finalizers = new Set();

  static #register(transient, external) {
    // https://v8.dev/features/weak-references
    const weakRef = new WeakRef(transient);
    const listener = () => {
      weakRef.deref()?.test();
    }
    external.addEventListener('testEvent', listener, { once: true });
    const finalizer = new FinalizationRegistry(({ external, listener, finalizer }) => {
      console.log("finalizing!");
      external.removeEventListener('testEvent', listener);
      this.#finalizers.delete(finalizer);
    });
    finalizer.register(transient, { external, listener, finalizer })
    this.#finalizers.add(finalizer);
  }

  constructor(external) {
    this.constructor.#register(this, external);
  }

  test() {
    console.log(`${this.test.name} called!`);
  }
}

async function main() {
  const external = new EventTarget();
 
  void function temp() {
    // this really must be GC'ed!
    new Transient(external);
  }();

  const gc = globalThis?.global?.gc;
  console.log(gc);
  await new Promise(r => setTimeout(() => r(gc?.(true)), 1000));
  await new Promise(r => setTimeout(() => r(gc?.(true)), 1000));
  await new Promise(r => setTimeout(() => r(gc?.(true)), 1000));

  external.dispatchEvent(new Event("testEvent"));

  console.log("done.")
}

main().catch(console.error);