BFE.devAI解答 - JavaScript 代码题
56. 调取有分页的API

使用常规循环解决：

async function fetchListWithAmount(amount: number = 5) {
  let lastItemId: number = undefined;
  let result: Array<{ id: number }> = [];

  while (result.length < amount) {
    const { items } = lastItemId ? await fetchList(lastItemId) : await fetchList();
    if (items.length === 0) {
      break;
    }
    lastItemId = items[items.length - 1].id;
    result = result.concat(items);
  }

  return result.slice(0, amount);
}

使用async iterators解决：

async function* itemGenerator() {
  let lastItemId: number = undefined;

  while (true) {
    const { items } = lastItemId ? await fetchList(lastItemId) : await fetchList();
    if (items.length === 0) {
      break;
    }
    lastItemId = items[items.length - 1].id;
    for (const item of items) {
      yield item;
    }
  }
}

async function fetchListWithAmount(amount: number = 5) {
  const result = [];
  const iterator = itemGenerator();
  for await (const item of iterator) {
    if (result.length >= amount) {
      break;
    }
    result.push(item);
  }
  return result;
}

使用async generators解决：

async function* itemGenerator(lastItemId?: number) {
  const { items } = lastItemId ? await fetchList(lastItemId) : await fetchList();
  if (items.length === 0) {
    return;
  }
  const newLastItemId = items[items.length - 1].id;
  for (const item of items) {
    yield item;
  }
  yield* itemGenerator(newLastItemId);
}

async function fetchListWithAmount(amount: number = 5) {
  const iterator = itemGenerator();
  const result = [];
  for (let i = 0; i < amount; i++) {
    const { done, value } = await iterator.next();
    if (done) {
      break;
    }
    result.push(value);
  }
  return result;
}