Nodejs get throw er; // Unhandled 'error' event [duplicate]

this is my firs program on NodeJs and i', trying to use Express and Socket.io on that. after create simple project as below code, i get

throw er; // Unhandled 'error' event

error, i'm google more tutorials but i cant find whats my code problem

install packages:

{
    "name": "signalAndroidServerApplication",
    "version": "0.0.0",
    "private": true,
    "dependencies": {
        "body-parser": "~1.12.4",
        "cookie-parser": "~1.3.5",
        "express": "~4.12.4",
        "socket.io": "latest"
    }
}

my nodejs:

var socket = require('socket.io');
var express = require('express');
var app = express();
var server = require('http').createServer(app);
var io = socket.listen(server);
var port = process.env.PORT || 3000;

server.listen(port, function () {
    console.log('Server listening at port %d', port);
});

io.on('connection', function (socket) {
    socket.on('new_count_message', function (data) {
        console.log('new_count_message' + data);
        io.sockets.emit('new_count_message', {
            new_count_message: data.new_count_message
        });
    });
});

full error:

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: listen EADDRINUSE
    at errnoException (net.js:901:11)
    at Server._listen2 (net.js:1039:14)
    at listen (net.js:1061:10)
    at Server.listen (net.js:1135:5)
    at Object.<anonymous> (/var/www/signal/nodeJs/server.js:8:8)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)