$("#form").submit(function(e) {
  e.preventDefault()
  var xhr = new XMLHttpRequest();
  var params = $('#form').serialize();
  xhr.open('POST', '/mail.php', true);
  xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
  xhr.onreadystatechange = function() {
    if (xhr.readyState == 4) {
       if(xhr.status == 200) {
       $('#form').css("display", "none");
           }
    }
  };
  xhr.send(params);
});