Андрей

// node.js: 10.15.3
// express: 4.16.4
// mongoose: 5.9.6

const mongoose = require('mongoose');
let isFirstConnected = false;

mongoose.Promise = global.Promise;

function connectDB() {
  mongoose.connect(process.env.DATABASE, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  });
}

mongoose.connection.on('connected', () => {
  console.log(
    `Mongoose default connection open ${process.env.DATABASE}`,
  );
  isFirstConnected = true;
});

mongoose.connection.on('error', err => {
  console.log('Mongoose default connection error: ' + err);
  if (!isFirstConnected) {
    setTimeout(connectDB, 1000);
  }
});

mongoose.connection.on('disconnected', () => {
  console.log('Mongoose default connection disconnected');
});

connectDB();