Node入门中, 有关于阻塞与非阻塞。如果使用route来返回结果会阻塞, 而使用传递response的方式就不会阻塞，有谁能解释一下吗？

使用route返回结果会阻塞：

 function onRequest(request, response) {
        var pathname = url.parse(request.url).pathname;
        console.log('Request for ' + pathname + ' received.');
        var content = route(handler, pathname);
        response.writeHead(200, {'Content-Type':'text/plain'});
        response.write(content);
        response.end();
    }
    http.createServer(onRequest).listen(8888);
    console.log('Server started at port: 8888');

传递response则不会阻塞：

function onRequest(request, response) {
    var pathname = url.parse(request.url).pathname;
    console.log("Request for " + pathname + " received.");
    route(handle, pathname, response);
  }
  http.createServer(onRequest).listen(8888);
  console.log("Server has started.");

PS: js的异步与事件机制我了解，但是感觉这里http封装起来就看不懂那些地方是异步了。