Javascript 如何使用等待保存在mongoose 中

下面的代码可以工作，但我只想使用async/await，所以我的问题是:我如何才能转向

cat.save().then(() => console.log('Saved in db'));

变成用await来代替？

我有mongoose.connection.once()的原因是只有在连接MongoDB时才发送命令.如果这也能用await，那就太好了=)

import mongoose from 'mongoose';
import { connectDb } from './modules/connectDb';
const { Schema } = mongoose;
const catSchema = new Schema({ name: String });
    
(async () => {
  connectDb('testDB');

  mongoose.connection.once('open', () => {
    console.log('MongoDB is connected');

    mongoose.connection.db.listCollections().toArray(function (err, names) {
      console.log(names);
    });

    const catModel = mongoose.model('testColl', catSchema);

    const cat = new catModel({ name: 'Zildjian' });
    cat.save().then(() => console.log('Saved in db'));
  });
})();

connectDb.ts个

import mongoose from 'mongoose';
import { strict as assert } from 'assert';
import { readToml } from './readToml';

const db = readToml('./config/database.toml');

export function connectDb(
  database: string = db.database,
  uri: string = db.uri,
  username: string = db.username,
  password: string = db.password,
) {
  assert(typeof uri === 'string');
  assert(typeof database === 'string');
  assert(typeof username === 'string');
  assert(typeof password === 'string');

  const URI = `mongodb+srv://${username}:${password}@${uri}/${database}?retryWrites=true&w=majority`;

  try {
    mongoose.connect(URI);
  } catch (err) {
    console.error(err);
  }
}