如文档中所述，您可以在响应的nModified字段中获得更新文档的数量。
所以你可以这样访问它：

const response = await Employees.updateMany(
  {
    InsertDate: {
      $gte: _yesterday,  // date ojbect that is passed as a param
      $lte: _today  // date ojbect that is passed as a param
    }
  },
  { $set: { RegistrationDate: ... // some var that I generate } }
);

console.log("Number of updated documents: ", response.nModified);

如果您使用的是MongoDB版本〉= 5.0，则使用modifiedCount代替nModified
例如

const response = await Employees.updateMany(
  {
    InsertDate: {
      $gte: _yesterday,  // date ojbect that is passed as a param
      $lte: _today  // date ojbect that is passed as a param
    }
  },
  { $set: { RegistrationDate: ... // some var that I generate } }
);

console.log("Number of updated documents: ", response.modifiedCount);