表单没有'不能正确执行请求后功能

由于某些未知原因，此表单无法按照Send((函数中的设置发出正确的POST请求，无法找出原因，尝试了所有方法。

$http.post(url,data,callback);函数可以工作，我通过控制台用相同的数据测试了它，但不知何故，当它被调用onsubmit时，什么都没有发生。POST请求不会发生，服务器也不会接收或记录任何内容。有人能对这个谜团提供一些见解吗？

服务器是Express的节点//我们只说这是服务器处理后请求的方式，只是为了测试

  app.post('/signin',function (req,res) {
   res.send('It works!');
   console.log(req.body);
  });
  app.post('/signup',function (req,res) {
    res.send('It works!');
    console.log(req.body);
  });

这是HTML表单

  <div class="auth-form">
  <label class="auth-form-tab">Sign In</label>
  <label class="auth-form-tab">Sign Up</label>
  <form onsubmit="Send();return false;">
    <input type="text"  name="username"  placeholder="Username">
    <input type="text"  name="firstname" placeholder="First Name">
    <input type="text"  name="lastname"  placeholder="Last Name">
    <input type="email" name="email"     placeholder="Email">
    <input type="password" name="password" placeholder="Password">
    <input type="submit">
  </form>
  <div class="status"></div>
 </div>
 <script src="/js/auth.js">

这里是JS，忽略AppScope.ActiveTab的事情它不应该影响任何

function Send() {
  if (AppScope.ActiveTab == 'SignIn') {
    $http.post('/signin', AppScope.FormData, function (data) {
      console.log(data);
      document.querySelector('.status').innerHTML = data;
    });
  } else {
    $http.post('/signup', AppScope.FormData, function (data) {
      console.log(data);
      document.querySelector('.status').innerHTML = data;
    });
  }
}
var AppScope = {
  ActiveTab: 'SignIn',
  Status: '',
  FormData: {
    username: document.querySelector('input[name=username]').value,
    firstname: document.querySelector('input[name=firstname]').value,
    lastname: document.querySelector('input[name=lastname]').value,
    email: document.querySelector('input[name=email]').value,
    password: document.querySelector('input[name=password]').value
  }
};
var $http = {};
$http.serialiseObject = function (obj) {
  var pairs = [];
  for (var prop in obj) {
    if (!obj.hasOwnProperty(prop)) continue;
    if (Object.prototype.toString.call(obj[prop]) == '[object Object]') {
      if (obj[prop] !== null) {
        pairs.push($http.serialiseObject(obj[prop]));
        continue;
      }
    }
    if (obj[prop] !== null) pairs.push(prop + '=' + obj[prop]);
  }
  return pairs.join('&');
};
$http.post = function (url, data, callback) {
  if (url == undefined) return Error('URL undefined');
  if (data == undefined) return Error('can''t send nothing');
  var Req = new XMLHttpRequest();
  Req.open('POST', url, true);
  Req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
  Req.onreadystatechange = function () {
    if (Req.readyState == 4 && Req.status == 200) {
      var response = 'response' in Req ? Req.response : Req.responseText;
      if (callback) {
        callback(response);
      } else {
        Error('No Callback Found');
      }
    }
  };
  Req.send($http.serialiseObject(data));
};