is there a mongoose connect error callback

When you connect you can pick up the error in the callback:

mongoose.connect('mongodb://localhost/dbname', function(err) {
if (err) throw err;
});

In case anyone happens upon this, the version of Mongoose I'm running (3.4) works as stated in the question. So the following can return an error.

connection.on('error', function (err) { ... });

Late answer, but if you want to keep the server running you can use this:

mongoose.connect('mongodb://localhost/dbname',function(err) {
if (err)
return console.error(err);
});

there many mongoose callback you can use,

// CONNECTION EVENTS
// When successfully connected
mongoose.connection.on('connected', function () {
console.log('Mongoose default connection open to ' + dbURI);
});


// If the connection throws an error
mongoose.connection.on('error',function (err) {
console.log('Mongoose default connection error: ' + err);
});


// When the connection is disconnected
mongoose.connection.on('disconnected', function () {
console.log('Mongoose default connection disconnected');
});


// If the Node process ends, close the Mongoose connection
process.on('SIGINT', function() {
mongoose.connection.close(function () {
console.log('Mongoose default connection disconnected through app termination');
process.exit(0);
});
}); 

more on: http://theholmesoffice.com/mongoose-connection-best-practice/

As we can see on the mongoose documentation for Error Handling, since the connect() method returns a Promise, the promise catch is the option to use with a mongoose connection.

So, to handle initial connection errors, you should use .catch() or try/catch with async/await.

In this way, we have two options:

Using the .catch() method:

mongoose.connect('mongodb://localhost:27017/test', { useNewUrlParser: true })
.catch(error => console.error(error));

or using try/catch:

try {
await mongoose.connect('mongodb://localhost:27017/test', { useNewUrlParser: true });
} catch (error) {
console.error(error);
}

IMHO, I think that using catch is a cleaner way.

• Handle (catch) the connect exceptions
• Handle other connection errors
• show a message when successfully connected

mongoose.connect(
"mongodb://..."
).catch((e) => {
console.log("error connecting to mongoose!");
});
mongoose.connection.on("error", (e) => {
console.log("mongo connect error!");
});
mongoose.connection.on("connected", () => {
console.log("connected to mongo");
});