Using FormData bounding to a form element - The FormData interface provides a way to easily construct a set of key/value pairs representing form fields and their values, which can then be easily sent using the XMLHttpRequest.send() method.
var formObject = document.getElementById("idform");
formObject.addEventListener("submit", function(eventObject) {
eventObject.preventDefault(); // Do not submit the form.
const xhr = new XMLHttpRequest();
xhr.addEventListener("load", function() { // XMLHttpRequest events: readystatechange, load, error, ...
... // xhr.responseText
});
xhr.open("post", ...);
xhr.send(new FormData(formObject));
});