how can i set a callback for the error handling if mongoose isn't able to connect to my DB?

i know of

connection.on('open', function () { ... });

but is there something like

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


Solution 1

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

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

Solution 2

there many mongoose callback you can use,

// 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'); 

more on:

Solution 3

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) { ... });

Solution 4

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) {

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

Solution 5

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);

Solution 6

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