To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.

mongoose報錯：DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
其實我們閱讀報的警告就可以解決:在mongoose連接的時候在第二個參數的對象中加入

  useUnifiedTopology: true   

即為：

mongoose.connect(dbConfig.dbs, {
  useNewUrlParser: true,
  useUnifiedTopology: true     //這個即是報的警告
}).then(res => {
  console.log('數據庫連接成功')
})