The keystone of AJAX is the XMLHttpRequest object.
The XMLHttpRequest Object
All modern browsers support the XMLHttpRequest object.
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.
Create an XMLHttpRequest Object
All modern browsers (Chrome, IE7+, Firefox, Safari, and Opera) have a built-in XMLHttpRequest object.
Syntax for creating an XMLHttpRequest object:
variable = new XMLHttpRequest();
Old versions of Internet Explorer (IE5 and IE6) use an ActiveX Object:
variable = new ActiveXObject("Microsoft.XMLHTTP");
To handle all 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 xhttp;
if (window.XMLHttpRequest) {
xhttp = new XMLHttpRequest();
} else {
// code for IE6, IE5 xhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
In the next chapter you will learn about sending server requests.
