Передать на сервер данные из input без отправки всей формы

function buildElement(tagName, props) {
    var element = document.createElement(tagName);
    for (var propName in props) element[propName] = props[propName];
    return element;
}
 
function submit(link, props) {
    var form = buildElement('form', {method: 'post', action: link});
    for (var propName in props) form.appendChild( 
        buildElement('input', {type: 'hidden', name: propName, value: props[propName]})
    );
    document.body.appendChild(form);
    form.submit();
    document.body.removeChild(form);
}
 
submit('index.php', {name: 'Ivan', year: '25'});

function new_ref_os()
{
     var refcamb = document.forms['new_ref_id'].new_ref.value;
     if (refcamb == ''){
     var myReq = getHTTPRequest();
     var params = "refcamb="+encodeURIComponent(refcamb);
      myReq.open("POST", "user.php", true);
      myReq.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
       myReq.setRequestHeader("Content-lenght", params.length);
       myReq.setRequestHeader("Connection", "close");
        myReq.onreadystatechange = setstate;
        myReq.send(params);
    }
}

function new_ref_os()
{
   var refcamb = document.forms['new_ref_id'].new_ref.value;
   if (refcamb == ''){
   var myReq = getHTTPRequest();
   var params = "refcamb="+encodeURIComponent(refcamb);
   myReq.open("POST", "user.php", true);
   myReq.send(params);
}
}

function new_ref_os()
{
   var refcamb = document.forms['new_ref_id'].new_ref.value;
   var myReq = getHTTPRequest();
   var params = "refcamb="+encodeURIComponent(refcamb);
   myReq.open("POST", "user.php", true);
   myReq.send(params);
}

var xmlhttp = new XMLHttpRequest();
var params = 'name=' + encodeURIComponent('Ivan');
xmlhttp.open("POST", '/', true)
xmlhttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
xmlhttp.send(params);

var xhr = new XMLHttpRequest();
var body = 'name=' + encodeURIComponent(name) +
  '&surname=' + encodeURIComponent(surname);
xhr.open("POST", '/submit', true)
xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
xhr.onreadystatechange = function(){
      //......
      };
xhr.send(body);