未知列未定义

Question

I'm trying to make a shopping cart using node, SQL, and jade. Everything work sure, but when I reload the page items count in cart is increasing.

I try to make an ajax queries and when I send dates on server I see the error like unknown column undefined in 'where clause'. But when I try to send it without ajax everything working okay. Also it working okay when I send it from ejs template. So, which issue I made?

node.js code

var express = require('express');
var router = express.Router();
var mysql = require('mysql');
var session = require('express-session');

var conn = require('./connection');
var connection = conn.connection();

var data;

connection.query('SELECT * FROM products', function (err, rows) {
    if (err) throw err;
    data = rows;
});

router.use(session({
    secret: 'keyboard cat',
    resave: false,
    saveUninitialized: true
}));

var cart_data, cart = {};

router.post('/checkout', function (req, res) {
    cart = req.session.cart;
    if (!cart) {
        cart = req.session.cart = {}
    }

    var id = req.body.id;
    var count = parseInt(req.body.count, 10);

    cart[id] = (cart[id] || 0) + count;

    var ids = Object.keys(cart);

    if (ids.length > 0) {
        connection.query('SELECT * FROM products WHERE id IN (' + ids + ')', function (err, rows) {
            if (err) throw err;
            cart_data = rows;
            res.render('index', {title: 'Shopping', data: data, currency: 'Rub. ', cart_data: rows, cart: cart});
        });
    } else {
        res.render('index', {title: 'Shopping', data: data, currency: 'Rub. ', cart_data: cart_data});
    }
});

router.get('/checkout', function (req, res) {
    res.render('index', {title: 'Node Shopping', data: data, currency: 'Rub. ', cart_data: cart_data, cart: cart});
});

jade

extends layout

block content
    div(class='container')
        h1= title
        p Welcome to #{title}
        div(class='items')
each item in data
div(class='item')
h3=item.name
p=item.description
div(class='price')
 span=currency + item.price
 div(class='form-items')
  input(type='text', name='count', value='1')
  button(type='submit', class='item-select', onclick='showCustomer()', name='id', id='#{item.id}', value='#{item.id}')'add to cart'

ajax

function showCustomer(str) {
  var xhttp;
  if (str == "") {
    document.getElementById("txtHint").innerHTML = "";
    return;
  }
  xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
    document.getElementById("txtHint").innerHTML = this.responseText;
    }
  };
  xhttp.open("POST", "/checkout", true);
  xhttp.send();
}

Thanks