How do I catch node.js/express server errors like EADDRINUSE?

Question

This is my code.

if !module.parent
    try
        hons_server.listen config.port
        console.log 'Listening to port ' + config.port
    catch err
        console.error "Couldn't start server: #{String(err)}".red

hons_server is an express.js server. I'm having a hard time understanding why errors thrown as a result of hons_server.listen() aren't caught by the try/catch. When I run my server twice I get the output:

$ coffee src/server.coffee
Listening to port 9090

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
Error: listen EADDRINUSE
    at errnoException (net.js:632:11)
    at Array.0 (net.js:733:26)
    at EventEmitter._tickCallback (node.js:192:40)

I'd like to know why the thrown error isn't caught, and how/where I can catch the EADDRINUSE error.

Solution 1

Listen for the error event on the server isntance

hons_server.on 'error', (err) ->
    console.log 'there was an error:', err.message

Solution 2

The accepted solution did not work for me on nodejs 0.8.22 and express 3.1.0.

This did the trick:

process.on('uncaughtException', function(err) {
    if(err.errno === 'EADDRINUSE')
         console.log(...);
    else
         console.log(err);
    process.exit(1);
});     

Also see Node.js Express app handle startup errors

Comments

[Hubro]

Out of curiosity, how did you know that? I know it wasn't in the documentation and I can't find anything on which events the express server supports

[Linus Thiel]

Basically, the express server is the http Server, which is an event emitter.

[Hubro]

Does this still work in the newest version of Node? Please check out the answer below and update yours if needed.

[fent]

It still works. from express 3.0.0 and onwards, the express object no longer inherits from http.Server, it's just a function that gets plugged into a server. The error event would have to be listened on from the server object, not the express function.

[The Red Pea]

I expected the express server.listen(function(err){...} callback to support checking for errors, but this suggestion to listen for events like server.on('error', function(err){...}) work very well

[Agustín Clemente]

It works on vscode console, but in Windows cmd not, why is it?