index.js

var app = module.exports = require("koa")();

var html = 
    `<html>
        <head>
            <meta charset="UTF-8">
            <title>A small test page</title>
            <script src="//localhost:9091"></script>
        </head>
        <body>
            Page loaded at: <span id="demo"></span>
        </body>
        <script language="javascript">
                document.getElementById('demo').innerHTML = new Date();
        </script>
    </html>`;

app.use(function *(){
	if(this.request.path === "/client"){
		this.body = html;
		return;
	}
	this.body = "Koa says Hi!";
});

var port = process.env.PORT || (process.argv[2] || 3000);
port = (typeof port != "number") ? port : 3000;
 
if(!module.parent){ app.listen(port); }

console.log("Application started. Listening on port:" + port);