Heroku Node.js error: ReferenceError: server is not defined

Here's my app app.js:

var express=        require("express");

var app=    express();
app.get('/',function(req,res){
    console.log(req);
    res.send("Hello world");
});

app.get('*', function(req, res){
  res.send("Nothing to see here.", 404);
});

var port=   process.env.PORT || 3000;
app.listen(port,function(){
    var host=   server.address().address;
    var port=   server.address().port;
});

When I run nodejs app.js locally, this works as intended. I can go to localhost:3000 and see Hello world, but when I push this to Heroku, I get this in my log:

2016-10-25T03:37:09.449732+00:00 heroku[web.1]: Starting process with command `node app.js`
2016-10-25T03:37:11.207319+00:00 app[web.1]: /app/app.js:47
2016-10-25T03:37:11.207341+00:00 app[web.1]:    var host=   server.address().address;
2016-10-25T03:37:11.207342+00:00 app[web.1]:                                ^
2016-10-25T03:37:11.207343+00:00 app[web.1]: 
2016-10-25T03:37:11.207343+00:00 app[web.1]: ReferenceError: server is not defined
2016-10-25T03:37:11.207344+00:00 app[web.1]:     at Server.<anonymous> (/app/app.js:47:28)
2016-10-25T03:37:11.207345+00:00 app[web.1]:     at Server.g (events.js:291:16)
2016-10-25T03:37:11.207345+00:00 app[web.1]:     at emitNone (events.js:86:13)
2016-10-25T03:37:11.207346+00:00 app[web.1]:     at Server.emit (events.js:185:7)
2016-10-25T03:37:11.207346+00:00 app[web.1]:     at emitListeningNT (net.js:1278:10)
2016-10-25T03:37:11.207347+00:00 app[web.1]:     at _combinedTickCallback (internal/process/next_tick.js:71:11)
2016-10-25T03:37:11.207348+00:00 app[web.1]:     at process._tickCallback (internal/process/next_tick.js:98:9)
2016-10-25T03:37:11.207349+00:00 app[web.1]:     at Module.runMain (module.js:592:11)
2016-10-25T03:37:11.207349+00:00 app[web.1]:     at run (bootstrap_node.js:394:7)
2016-10-25T03:37:11.207350+00:00 app[web.1]:     at startup (bootstrap_node.js:149:9)
2016-10-25T03:37:11.287706+00:00 heroku[web.1]: State changed from starting to crashed
2016-10-25T03:37:11.290415+00:00 heroku[web.1]: Process exited with status 1

What's going on here?