nodejs mongodb官方节点包-异步函数不返回数据

const MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://localhost:27017', (err, client) => {
  if (err) {
    console.error(err);
    return;
  }

  const db = client.db('mydb');
  const collection = db.collection('mycollection');

  collection.find({}).toArray((err, docs) => {
    if (err) {
      console.error(err);
      return;
    }

    console.log(docs);
    client.close();
  });
});

const MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://localhost:27017')
  .then((client) => {
    const db = client.db('mydb');
    const collection = db.collection('mycollection');

    return collection.find({}).toArray();
  })
  .then((docs) => {
    console.log(docs);
  })
  .catch((err) => {
    console.error(err);
  });