NodeJS server executes two times?

I tried to develop a basic HTTP server with follow code:

var http = require("http");

http.createServer(function(request, response) {
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.write("Hello World");
    response.end();
}).listen(8888);

And works fine and page return: Hello World

After that i tried to understand the infinite cycle in NodeJS server and discover that: when use this code:

var http = require("http");
var n = 1;

http.createServer(function(request, response) {
    n++;
    response.writeHead(200, {"Content-Type": "text/plain"});
    response.write("Hello World");
    console.log('call: %d', n);
    response.end();
}).listen(8888);

And works fine page return: Hello World

But seeing the log i found a strange result, when page refresh. call: 2 call: 3 Basically at every call (page refresh) the server executes two times, why? This is the number of threads that run at every call?