奇怪的Promise链接情况: then()参数未定义，未返回最后一个链数据[重复]

new Promise((resolve, reject) => {
  resolve('initial data');
})
.then(data => {
  console.log(data); // 'initial data'
  return 'first then';
})
.then(data => {
  console.log(data); // 'first then'
  return 'second then';
})
.then(data => {
  console.log(data); // 'second then'
});

new Promise((resolve, reject) => {
  resolve('initial data');
})
.then(data => {
  console.log(data); // 'initial data'
  if (data === 'initial data') {
    throw new Error('Data is initial data');
  }
  return 'first then';
})
.catch(error => {
  console.error(error); // Error: Data is initial data
})
.then(data => {
  console.log(data); // undefined
  return 'second then';
})
.then(data => {
  console.log(data); // 'second then'
});

new Promise((resolve, reject) => {
  resolve('initial data');
})
.then(data => {
  console.log(data); // 'initial data'
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve('first then');
    }, 1000);
  });
})
.then(data => {
  console.log(data); // 'first then'
  return 'second then';
})
.then(data => {
  console.log(data); // 'second then'
});