is there a mongoose connect error callback

how开发者_开发知识库 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) { ... });

?

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

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

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) { ... });

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.

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);
});

• 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");
});