添加async和await关键字后，ajax函数无法工作

function ajax(url) {
  return new Promise((resolve, reject) => {
    const xhr = new XMLHttpRequest();
    xhr.open('GET', url, true);
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4) {
        if (xhr.status === 200) {
          resolve(xhr.responseText);
        } else {
          reject(new Error(xhr.statusText));
        }
      }
    };
    xhr.send();
  });
}

async function fetchData() {
  try {
    const response = await ajax('https://example.com/api/data');
    console.log(response);
  } catch (error) {
    console.error(error);
  }
}

fetchData();