Chained Promise で未定義の値が発生する原因とその修正方法

<code class="js">const doStuff = (n /* `n` is expected to be a positive number */) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve(n * 10);
    }, Math.floor(Math.random() * 1000));
  })
    .then((result) => {
      if (result > 100) {
        console.log(`${result} is greater than 100`);
      } else {
        console.log(`${result} is not greater than 100`);
      }
      // Return `result` to pass it to the next `.then()`
      return result;
    });
};

doStuff(9)
  .then((data) => {
    console.log("data is: " + data);
  });</code>