如何在不使用async await的情况下，使用javascript正确地调用两个REST API？

// 调用第一个REST API
function callFirstAPI() {
  return new Promise(function(resolve, reject) {
    fetch('https://api.example.com/first-api')
      .then(function(response) {
        if (response.ok) {
          resolve(response.json());
        } else {
          reject(new Error('API request failed'));
        }
      })
      .catch(function(error) {
        reject(error);
      });
  });
}

// 调用第二个REST API
function callSecondAPI() {
  return new Promise(function(resolve, reject) {
    fetch('https://api.example.com/second-api')
      .then(function(response) {
        if (response.ok) {
          resolve(response.json());
        } else {
          reject(new Error('API request failed'));
        }
      })
      .catch(function(error) {
        reject(error);
      });
  });
}

// 调用两个REST API
function callAPIs() {
  callFirstAPI()
    .then(function(firstAPIResponse) {
      console.log('First API response:', firstAPIResponse);
      return callSecondAPI();
    })
    .then(function(secondAPIResponse) {
      console.log('Second API response:', secondAPIResponse);
    })
    .catch(function(error) {
      console.error('API call failed:', error);
    });
}

// 调用函数
callAPIs();