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Ajax code

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The keystone of AJAX is the XMLHttpRequest object.
Different browsers use different methods to create the XMLHttpRequest object.
Internet Explorer uses an ActiveXObject, while other browsers uses the built-in JavaScript object called XMLHttpRequest.
 
<html>
<body>
<script type="text/javascript">
function ajaxFunction()
  {
  var xmlHttp;
  try
    {
    // Firefox, Opera 8.0+, Safari
    xmlHttp=new XMLHttpRequest();
    }
  catch (e)
    {
    // Internet Explorer
    try
      {
      xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
      }
    catch (e)
      {
      try
        {
        xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
      catch (e)
        {
        alert("Your browser does not support AJAX!");
        return false;
        }
      }
    }
  }
</script>
<form name="myForm">
Name: <input type="text" name="username" />
Time: <input type="text" name="time" />
</form>
</body>
</html>
 
Example explained: First create a variable xmlHttp to hold the XMLHttpRequest object.
Then try to create the object with XMLHttp=new XMLHttpRequest(). This is for the Firefox, Opera, and Safari browsers. If that fails, try xmlHttp=new ActiveXObject("Msxml2.XMLHTTP") which is for Internet Explorer 6.0+, if that also fails, try xmlHttp=new ActiveXObject("Microsoft.XMLHTTP") which is for Internet Explorer 5.5+
If none of the three methods work, the user has a very outdated browser, and he or she will get an alert stating that the browser doesn't support AJAX.
Note: The browser-specific code above is long and quite complex. However, this is the code you can use every time you need to create an XMLHttpRequest object, so you can just copy and paste it whenever you need it. The code above is compatible with all the popular browsers: Internet Explorer, Opera, Firefox, and Safari.
The next chapter shows how to use the XMLHttpRequest object to communicate with the server.
 
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