client.js

  var data={ foo:"bar"};
  var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      console.log("OK");
    }
  };
  xhttp.open("POST", "http://localhost:8080", true);
  xhttp.setRequestHeader("Content-type", "application/json");
  xhttp.send(JSON.stringify(data));

server.js

var http = require('http');
http.createServer(function (req, res) {
	res.write('Hello World!');
	req.on('data', function (chunk) {
		if (req.method == 'POST') {
			 console.log(chunk.toString());
		}
	});
	res.end();
}).listen(8080);