xhr.js

xhr.js

var form = new FormData;
var xhr = new XmlHttpRequest;
xhr.open('path/to/api', 'POST', true);
xhr.onreadystatechange = function(e) {
  console.log(e); // Check success/fail
}

var toSendData = {
  proName: [
    'Product 1',
    'Product 2'
  ],
  proDesc: ['', ''],
  amount: [10.0, 15.5],
  discount: [0, 0],
  total: [10.0, 15.5]
};

for(var i in toSendData) {
  form.append(i, toSendData[i]);
}

xhr.send(form);

var form = new FormData(document.forms[0]);
...
xhr.send(form);