您可以使用await关键字暂停**alwaysRuns（）函数的执行，直到第二次fetch（）调用完成。下面是alwaysRuns（）**函数的更新版本，它可以完成此操作：

async function alwaysRuns() {
  // Make the function asynchronous so we can use `await`
  const result = await fetch('https://api.spacexdata.com/v4/launches/latest');
  const resultJson = await result.json();
  const rocketId = resultJson.rocket;
  const rocketName = resultJson.name;

  if(rocketName.includes('Crew')) {
    const rocketResponse = await fetch(`https://api.spacexdata.com/v4/rockets/${rocketId}`);
    const rocketJson = await rocketResponse.json();
    console.log('This fetch might not happen, depending on the conditional')
  }

  console.log('this should always log last whether the conditional causes the second fetch to run or not!');
}

alwaysRuns();

await关键字用于暂停**alwaysRuns（）函数的执行，直到fetch（）调用完成并且它返回的承诺得到解决。这确保了第二个fetch（）调用在最后一个console.log（）**语句执行之前完成。

Use await

function alwaysRuns() {
  fetch('https://api.spacexdata.com/v4/launches/latest')
    .then(result => result.json())
    .then(async resultJson => {
      const rocketId = resultJson.rocket;
      const rocketName = resultJson.name;
      if(rocketName.includes('Crew')) {
        await fetch(`https://api.spacexdata.com/v4/rockets/${rocketId}`)
          .then(rocketResponse => rocketResponse.json())
          .then(rocketJson => {
            console.log('This fetch might not happen, depending on the conditional')
        });
      }
      console.log('this should always log last whether the conditional causes the second fetch to run or not!');
  });
}
alwaysRuns();

or even better

function alwaysRuns() {
  fetch('https://api.spacexdata.com/v4/launches/latest')
    .then(result => result.json())
    .then(resultJson => {
      const rocketId = resultJson.rocket;
      const rocketName = resultJson.name;
      if(rocketName.includes('Crew')) {
        return fetch(`https://api.spacexdata.com/v4/rockets/${rocketId}`)
          .then(rocketResponse => rocketResponse.json())
          .then(rocketJson => {
            console.log('This fetch might not happen, depending on the conditional')
        });
      }
    }).then(() => {
    console.log('this should always log last whether the conditional causes the second fetch to run or not!');
  });
}
alwaysRuns();