Request a callback when registered objects are all garbage-collected

GroupFinalizationRegistry.ts

export default class GroupFinalizationRegistry<T> extends FinalizationRegistry<T> {
  #members: WeakRef<object>[] = [];

  constructor(cleanupCallback: (heldValue: T) => void) {
    super((heldValue) => {
      if (this.#members.length === 0) return;
      this.#members = this.#members.filter((member) => (
        member.deref() !== undefined
      ));
      if (this.#members.length === 0) {
        this.#tokenMembersMap = new WeakMap();
        cleanupCallback(heldValue);
      }
    });
  }

  #tokenMembersMap: WeakMap<object, WeakRef<object>[]> = new WeakMap();

  register(target: object, heldValue: T, unregisterToken?: object) {
    super.register(target, heldValue, unregisterToken);
    const member = new WeakRef(target);
    this.#members.push(member);
    if (unregisterToken !== undefined) {
      const tokenMembers = this.#tokenMembersMap.get(unregisterToken);
      if (tokenMembers) {
        tokenMembers.push(member);
      } else {
        this.#tokenMembersMap.set(unregisterToken, [member]);
      }
    }
  }

  unregister(unregisterToken: object) {
    super.unregister(unregisterToken);
    const tokenMembers = this.#tokenMembersMap.get(unregisterToken);
    if (tokenMembers === undefined) return false;
    this.#members = this.#members.filter((member) => (
      !tokenMembers.includes(member)
    ));
    this.#tokenMembersMap.delete(unregisterToken);
    return true;
  }
}