谷歌地图方向服务，如何等待所有请求完成？

// 使用Promise对象
function getAllDirections(requests) {
  const promises = requests.map(request => {
    return new Promise((resolve, reject) => {
      // 发送请求
      // ...
      // 请求完成后调用resolve
      // ...
    });
  });

  return Promise.all(promises);
}

// 使用async/await
async function getAllDirections(requests) {
  const results = [];

  for (const request of requests) {
    const result = await sendRequest(request);
    results.push(result);
  }

  return results;
}

// 使用回调函数
function getAllDirections(requests, callback) {
  const results = [];

  let count = 0;
  for (const request of requests) {
    sendRequest(request, (error, result) => {
      if (error) {
        callback(error);
        return;
      }

      results.push(result);
      count++;

      if (count === requests.length) {
        callback(null, results);
      }
    });
  }
}

// 使用Promise对象
function getAllDirections(requests) {
  const promises = requests.map(request => {
    return new Promise((resolve, reject) => {
      sendRequest(request, (error, result) => {
        if (error) {
          reject(error);
          return;
        }

        resolve(result);
      });
    });
  });

  return Promise.all(promises);
}