var xmlRequest = new XMLHttpRequest();

function getUserListAsHTML()
{
    var userList = "";

    xmlRequest.open("GET", "listUsers.php", true);

    xmlRequest.onreadystatechange=function() {
     if(xmlRequest.readyState == 4 && xmlRequest.status == 200) {
      document.getElementById("userList").innerHTML = xmlRequest.responseText;
     }
    }

    xmlRequest.send();
}



getUserListAsHTML();

setTimeout(getUserListAsHTML(), 1000);