如何在node.js中响应XMLHttpRequest

Question

通过XMLHttpRequest，我用

发送一些数据

 const xhr = new XMLHttpRequest()

  xhr.onreadystatechange = function (event) {
    if (xhr.readyState === 4 /** responseText is not available yet */) {
      const statusCode = xhr.status
      const responseText = xhr.responseText
      // some callback functions
    }
  }
  xhr.open('POST', url, true /** async */)
  xhr.setRequestHeader('Content-Type', 'text/plain')
  xhr.withCredentials = true 
  xhr.timeout = timeoutMillis 
  xhr.ontimeout = function (event) {
    // some time out error log
  }
  xhr.send(JSON.stringify(payloads))

和服务器端node.js服务器代码是

   var httpPort = 3001
var http = require('http')
   ,qs = require('querystring');
http.createServer(function (req, res) {
        console.log(req.url + " "  + req.method);
   if( req.url == '/mytoken' && req.method == 'POST'){
        console.log('start');
        var body = [];
        res.writeHead(200, {'Content-Type':'text/plain'});
        req.on('data', function(chunk){
                body.push(chunk);
                console.log('GOT DATA: ' + body);
        });
        res.end('OK');
   }else{
        res.writeHead(404, {'Content-Type': 'text/plain'});
        res.end('404 ERROR');
   }
}).listen(httpPort);

我写了这样的服务器代码。但是，服务器没有发送任何响应。

应该是statusCode 200 with responseText＆＃39; OK＆＃39;。

我错过了一些？或做错了吗？

编辑1：编辑服务器代码并读取发送给我的数据