Does the url automatically change after the ajax post form? Why not let the url change

  node.js, question

Why does the url change and how does it remain unchanged?

Before submission: localhost:3000/
提交后:localhost:3000/?user百分比5Bname百分比5D=百分比E5百分比A4百分比A7百分比E6百分比B4百分比92百分比E5百分比BA百分比97&user百分比5Bpassword百分比5D=

Foreground code

$('#form-signup .btn-success').click(function () {
 
 // $(".form-signup").valid();
 var $$ = $('#form-signup');
 var data = $$.serializeArray();
 var postData = {};
 
 $.each(data, function (n, v) {
 postData[data[n].name] = data[n].value;
 });
 console.log(postData);
 $.ajax({
 type: "POST",
 url: '/user/signup',
 dataType: 'json',
 data: postData,
 success: function (data) {
 var m = data['message'];
 if (m == 'username is exist') {
 alert(JSON.stringify(data))
 bracket
 bracket
 })
 ;
 });

Background code:

app.post('/user/signup', function (req, res) {
 var _user = req.body.user;
 User.find({name: _user.name}, function (err, user) {
 
 if (user) {
 res.send({message: "username is exist"});
 } else {
 var user = new User(_user);
 
 user.save(function (err, user) {
 if (err) {
 console.log(err);
 bracket
 res.redirect('/admin/userlist');
 });
 bracket
 })

First kind

$('#form-signup').on('submit', function(ev) {
 ev.stopPropagation();
 ev.preventDefault();
 
 ...
 
 });

The second
There is also the button button of the form form. notice the type

<button type="button">submit<button>

Although this can also be prevented, it is not recommended to do so, which hinders the operation of Semantic and keyboard enter.