AJAX how to get response without html page?

Question

JavaScript

All the best.
I'm trying to make a form adding a product without reloading.
In all examples, this is based on three files:
1 - html form code
2 - javascript file
3 - php handler.
I have an html form and PHP handler is one file, the post request is sent to the address of the current page.
Attention to the question:
How to catch only the answer of the PHP script from the answer?
Now in the response comes the form html and the script response.
It is not possible to split into two files (php script form html).

$( document ).ready(function() {
document.getElementById('razmestit').addEventListener('submit', function(evt){
  var http = new XMLHttpRequest(), f = this;
  evt.preventDefault();
  http.open("POST", location.href, true);
  http.onreadystatechange = function() {
    if (http.readyState == 4 && http.status == 200) {
    alert(http.responseText);
          if (http.responseText.indexOf(f.name.value) !== 0) {
    $('input').val(``);
    $('textarea').val(``);
        }
    }
  }
  http.onerror = function() {
    alert('Что-то не так!');
  }
  http.send(new FormData(f));
}, false);
});

Answer 1

I asked myself, I will answer.
In the file with the html form, first the php handler with exit!

if (isset($_POST['name'])) {
  echo 'Ваше объявление добавлено и будет опубликовано после проверки.';
  exit();
}
html.......