(node) DeprecationWarning: current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the newServer Discover and Monitoring engine, pass option { useUnifiedTopology:true} to the MongoClient constructor.
第二个:
(node) DeprecationWarning: current URL string parser is deprecated, and will be removed in a future version. To use the newparser, pass option { useNewUrlParser:true} to MongoClient.connect.
第三个:
(node) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes