不同类型的ajax实现

我刚刚开始为我的聊天应用程序开发ajax，我正在php中制作这个应用程序。在网上学习ajax时，我在实现ajax的不同网站上通过两种方式进行了研究。这两种ajax实现之间有什么区别？任何帮助都将不胜感激：(

首次实施-

    <script type"text/javascript">
        $(document).ready(function() {
        var dept = '<?php echo $deptId; ?>';
        var interval = setInterval(function() {
            $.ajax({
                url: 'scripts/php/Chat.php',
                data: {dept:dept},
                success: function(data) {
                $('#messages').html(data);
            }
        });
        }, 1000);
    });
    </script>

第二次实施-

<script language="javascript" type="text/javascript">
function ajaxFunction(){
var ajaxRequest;  // The variable that makes Ajax possible!
try{
  // Opera 8.0+, Firefox, Safari
  ajaxRequest = new XMLHttpRequest();
}catch (e){
  // Internet Explorer Browsers
  try{
     ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
  }catch (e) {
     try{
        ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
     }catch (e){
        // Something went wrong
        alert("Your browser broke!");
        return false;
     }
  }
 }
// Create a function that will receive data
// sent from the server and will update
// div section in the same page.
ajaxRequest.onreadystatechange = function(){
  if(ajaxRequest.readyState == 4){
      var ajaxDisplay = document.getElementById('ajaxDiv');
      ajaxDisplay.innerHTML = ajaxRequest.responseText;
  }
}
// Now get the value from user and pass it to
// server script.
var age = document.getElementById('age').value;
var wpm = document.getElementById('wpm').value;
var sex = document.getElementById('sex').value;
var queryString = "?age=" + age ;
queryString +=  "&wpm=" + wpm + "&sex=" + sex;
ajaxRequest.open("GET", "ajax-example.php" + queryString, true);
ajaxRequest.send(null); 
}