AJAX - Creating the XMLHttpRequest Object

XMLHttpRequest is the foundation of AJAX.

XMLHttpRequest Object

All modern browsers support the XMLHttpRequest object (IE5 and IE6 use ActiveXObject).

XMLHttpRequest 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, Safari, and Opera) have a built-in XMLHttpRequest object.

The syntax for creating an XMLHttpRequest object:

Older versions of Internet Explorer (IE5 and IE6) use an ActiveX object:

To cope with 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:

Example

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");
}

In the next chapter, you will learn about sending server requests.