a.js

var koa = require('koa');
var app = new koa()
    // router = require('koa-router'),
    // serve = require('koa-static'),
    // views = require('koa-views');

// Send static files
// app.use(serve('./public'));

// Use jade
// app.use(views(__dirname +'/views', 'jade', {}));

// Router
// app.use(router(app));

// This must come after last app.use()
var server = require('http').Server(app.callback()),
    io = require('socket.io')(server);

/**
 * Routes can go both before and after but
 * app.use(router(app)); must be before
 */
app.use( (ctx) => {
    // yield this.render('index', { my: 'data' });
    ctx.body = 'hello world'
});

// Socket.io
io.on('connection', function(socket){
    socket.emit('news', { hello: 'world' });
    socket.on('my other event', function (data) {
        console.log(data);
    });
});

// Start the server
server.listen(1337);
console.info('Now running on localhost:1337');