V8 while await loop scope optimization issue. See https://bugs.chromium.org/p/v8/issues/detail?id=9101

v8-while-await-optimization-fail-1.js

function makeObserver(): [Promise<boolean>, FinalizationGroup<any>] {
  let resolve: (collected: boolean) => void;
  const collected = new Promise<boolean>(r => (resolve = r));
  const finalizationGroup = new FinalizationGroup<any>(items => {
    // Let's be nice and cleanup
    [...items];
    resolve(true);
  });
  return [collected, finalizationGroup];
}

async function gcOf_fail(target?: object): Promise<boolean> {
  const [collected, finalizationGroup] = makeObserver();
  finalizationGroup.register(target || {}, 0);
  target = undefined;

  let result: boolean | undefined;
  while (true) {
    result = await Promise.race([
      collected,
      new Promise<undefined>(resolve => setTimeout(resolve, 0))
    ]);
    if (result !== undefined) break;
    gc();
  }

  return result;
}

async function gcOf_success(target?: object): Promise<boolean> {
  const [collected, finalizationGroup] = makeObserver();
  finalizationGroup.register(target || {}, 0);
  target = undefined;

  let result: boolean | undefined;
  while (
    (result = await Promise.race([
      collected,
      new Promise<undefined>(resolve => setTimeout(resolve, 0))
    ])) === undefined
  ) {
    gc();
  }

  return result;
}

v8-while-await-optimization-fail-2.js

function makeObserver(): [{ collected: boolean }, FinalizationGroup<any>] {
  let token = { collected: false };
  const finalizationGroup = new FinalizationGroup<any>(items => {
    // Let's be nice and cleanup
    [...items];
    token.collected = true;
  });
  return [token, finalizationGroup];
}

async function gcOf_fail(target?: object): Promise<boolean> {
  const [token, finalizationGroup] = makeObserver();
  finalizationGroup.register(target || {}, 0);
  target = undefined;

  while (!token.collected) {
    await new Promise<undefined>(resolve => setTimeout(resolve, 0));
    gc();
  }

  return token.collected;
}

async function gcOf_success(target?: object): Promise<boolean> {
  const [token, finalizationGroup] = makeObserver();
  finalizationGroup.register(target || {}, 0);
  target = undefined;

  while ((await new Promise(resolve => setTimeout(resolve, 0)), !token.collected)) {
    gc();
  }

  return token.collected;
}