Can't capture duplicate port error in Express - node.js

Question

All,
I have a simple Express web server on Windows Node. I can't work out how to capture the error if I'm trying to start the server on the same port as another instance of Express already running. The error middleware won't capture it and the usual .on("error", function ()....) doesn't work either, and the whole Node application bombs - I want to capture it gracefully.
Here is the code:
var express = require('express');
var compression = require('compression')
var app = express();
var __dirname = ""
app.use(compression({ threshold: 512 }));
var oneYear = 86400000 * 365;
app.enable('etag')
app.use(express.static(__dirname + '../../HAWebClient', { maxAge: oneYear }));
app.use(function (err, req, res, next) {
if (!err) return next();
console.log('<-------Error Occured ----->');
res.send(500, JSON.stringify(err, ['stack', 'message']));
});
app.on("error", function (err) {
status("SYSTEM/HTTP", "Error with the web server: " + err);
// Do stuff with error
});
app.listen(80);
and I get
events.js:72
throw er; // Unhandled 'error' event
^
Error: listen EADDRINUSE
at errnoException (net.js:904:11)
at Server._listen2 (net.js:1042:14)
at listen (net.js:1064:10)
at Server.listen (net.js:1138:5)
at Function.app.listen (C:\Users\deandob\Documents\GitHub\PluginMgr\PluginMgr\node_modules\express\lib\application.js:546:24)
at webSvr (C:\Users\deandob\Documents\GitHub\PluginMgr\PluginMgr\PlugMgr.js:298:9)
at Object.<anonymous> (C:\Users\deandob\Documents\GitHub\PluginMgr\PluginMgr\PlugMgr.js:271:1)
at Module._compile (module.js:456:26)
at Object.Module._extensions..js (module.js:474:10)
at Module.load (module.js:356:32)
Press any key to continue...
Don't want to capture this in Node's global error handler (which loses error context) - this error should be able to be captured by app.on("error,....) but I'm obviously missing something here. Thanks for the input!

Answer 1

When the port is already in use, app.listen(80); will throw an exception asynchronously (the exception you see in your error log) if you don't have an error handler on the server. The server, in this case, is the return value from app.listen(), not the app object which is why you attempt at handling the error was not working.
Rather than let that exception go to the system which will shut-down your app, you can catch the error and prevent the exception like this:
var server = app.listen(8080);
server.on('error', function(e) {
console.log(e);
// put your code here
});
And, then decide what to do in the error handler. I have tested this solution in a sample server and it does work.
FYI, the relevant documentation is on the socket object here: https://nodejs.org/api/net.html#net_server_listen_port_host_backlog_callback