// use Promise.then()
gplay.list({
  country: 'tw',
  collection: gplay.collection.TOP_FREE,
  num: 100
}).then(value =>
  value.map(function (item) { return item['appId']; })
);

// use async/await
async function logTopFreeList() {
  const value = await gplay.list(/* 略www */);
  value.map(function (item) { return item['appId']; });
}

logTopFreeList();