how does mongoose ensure a connection is open code example

Example 1: mongoose connect to URL of atals

try {
  mongoose.connect(MONGODB_URI || 'mongodb://localhost/YOUR_DB_NAME', {
      useNewUrlParser: true,
      useUnifiedTopology: true
    }, () =>
    console.log("connected"));
} catch (error) {
  console.log("could not connect");
}

Example 2: mongoose connect

mongoose.connect('mongodb://username:password@host:port/database?options...', {useNewUrlParser: true});