Slide 13.3: AJAX creating an XMLHttpRequest object

AJAX Creating an XMLHttpRequest Object

Let AJAX change this text.

The XMLHttpRequest Object
The keystone of AJAX is the XMLHttpRequest object. All modern browsers support the XMLHttpRequest object (IE5 and IE6 uses an ActiveXObject). The XMLHttpRequest object is used to exchange data with a server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.

Creating an XMLHttpRequest Object
All modern browsers (IE7+, Firefox, Chrome, and Opera) have a built-in XMLHttpRequest object. Syntax for creating an XMLHttpRequest object is

   variable = new XMLHttpRequest( );

Old versions of Internet Explorer (IE5 and IE6) uses an ActiveXObject:

   variable = new ActiveXObject( "Microsoft.XMLHTTP" );

To handle all modern browsers, including IE5 and IE6, check if the browser supports the XMLHttpRequest object. If it does, create an XMLHttpRequest object, if not, create an ActiveXObject:

<script type="text/javascript">
  function loadXMLDoc( ) {
    var xmlhttp;
    if ( window.XMLHttpRequest ) {
      // code for IE7+, Firefox, Chrome, Opera, Safari
      xmlhttp = new XMLHttpRequest( );
    }
    else {
      // code for IE6, IE5
      xmlhttp = new ActiveXObject( "Microsoft.XMLHTTP" );
    }
    xmlhttp.onreadystatechange = function( ) {
      if ( ( xmlhttp.readyState == 4 ) && 
           ( xmlhttp.status     == 200 ) ) {
        document.getElementById("myDiv").innerHTML =
          xmlhttp.responseText;
      }
    }
    xmlhttp.open( "GET", "AJAX_info.txt", true );
    xmlhttp.send( );
  }
</script>