AJAX is not a new programming language, but a new technique for creating better, faster, and more interactive web applications.

With AJAX, a JavaScript can communicate directly with the server, with the XMLHttpRequest object. With this object, a JavaScript can trade data with a web server, without reloading the page.

AJAX uses asynchronous data transfer (HTTP requests) between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages.

The AJAX technique makes Internet applications smaller, faster and more user-friendly.

AJAX is based on Internet standards

AJAX is based on the following web standards:

    * JavaScript
    * XML
    * HTML
    * CSS

lamp  AJAX applications are browser- and platform-independent.
AJAX uses the XMLHttpRequest object

To get or send information from/to a database or a file on the server with traditional JavaScript, you will have to make an HTML form, and a user will have to click the "Submit" button to send/get the information, wait for the server to respond, then a new page will load with the results. Because the server returns a new page each time the user submits input, traditional web applications can run slowly and tend to be less user-friendly.

With AJAX, your JavaScript communicates directly with the server, through the JavaScript XMLHttpRequest object.

With the XMLHttpRequest object, a web page can make a request to, and get a response from a web server – without reloading the page. The user will stay on the same page, and he or she will not notice that scripts request pages, or send data to a server in the background.
The XMLHttpRequest object

By using the XMLHttpRequest object, a web developer can update a page with data from the server after the page has loaded!

AJAX was made popular in 2005 by Google (with Google Suggest).

Google Suggest is using the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google’s search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.

The XMLHttpRequest object is supported in all major browsers (Internet Explorer, Firefox, Chrome, Opera, and Safari).

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AJAX – More About the XMLHttpRequest Object

Before sending data to the server, we have to explain three important properties of the XMLHttpRequest object.
The onreadystatechange Property

After a request to the server, we need a function that can receive the data that is returned by the server.

The onreadystatechange property stores your function that will process the response from a server. This is not a method, the function is stored in the property to be called automatically. The following code sets the onreadystatechange property and stores an empty function inside it:

xmlHttp.onreadystatechange=function()
{
// We are going to write some code here
}

The readyState Property

The readyState property holds the status of the server’s response. Each time the readyState changes, the onreadystatechange function will be executed.

Here are the possible values for the readyState property:
State Description
0 The request is not initialized
1 The request has been set up
2 The request has been sent
3 The request is in process
4 The request is complete

We are going to add an If statement to the onreadystatechange function to test if our response is complete (this means that we can get our data):

xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
// Get the data from the server’s response
}
}

The responseText Property

The data sent back from the server can be retrieved with the responseText property.

In our code, we will set the value of our “time” input field equal to responseText:

xmlHttp.onreadystatechange=function()
{
if(xmlHttp.readyState==4)
{
document.myForm.time.value=xmlHttp.responseText;
}
}

The next chapter shows how to ask the server for some data!

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AJAX – Browser Support

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.

To create this object, and deal with different browsers, we are going to use a “try and catch” statement. You can read more about the try and catch statement in our JavaScript tutorial.

Let’s update our “testAjax.htm” file with the JavaScript that creates the XMLHttpRequest object:

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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AJAX Uses HTTP Requests

In traditional JavaScript coding, if you want to get any information from a database or a file on the server, or send user information to a server, you will have to make an HTML form and GET or POST data to the server. The user will have to click the “Submit” button to send/get the information, wait for the server to respond, then a new page will load with the results.

Because the server returns a new page each time the user submits input, traditional web applications can run slowly and tend to be less user-friendly.

With AJAX, your JavaScript communicates directly with the server, through the JavaScript XMLHttpRequest object

With an HTTP request, a web page can make a request to, and get a response from a web server – without reloading the page. The user will stay on the same page, and he or she will not notice that scripts request pages, or send data to a server in the background.
The XMLHttpRequest Object

By using the XMLHttpRequest object, a web developer can update a page with data from the server after the page has loaded!

AJAX was made popular in 2005 by Google (with Google Suggest).

Google Suggest is using the XMLHttpRequest object to create a very dynamic web interface: When you start typing in Google’s search box, a JavaScript sends the letters off to a server and the server returns a list of suggestions.

The XMLHttpRequest object is supported in Internet Explorer 5.0+, Safari 1.2, Mozilla 1.0 / Firefox, Opera 8+, and Netscape 7.

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AJAX stands for Asynchronous JavaScript And XML.
What You Should Already Know

Before you continue you should have a basic understanding of the following:

* HTML / XHTML
* JavaScript

If you want to study these subjects first, find the tutorials on our Home page.
AJAX = Asynchronous JavaScript and XML

AJAX is not a new programming language, but a technique for creating better, faster, and more interactive web applications.

With AJAX, your JavaScript can communicate directly with the server, using the JavaScript XMLHttpRequest object. With this object, your JavaScript can trade data with a web server, without reloading the page.

AJAX uses asynchronous data transfer (HTTP requests) between the browser and the web server, allowing web pages to request small bits of information from the server instead of whole pages.

The AJAX technique makes Internet applications smaller, faster and more user-friendly.

lamp  AJAX is a browser technology independent of web server software.
AJAX is Based on Web Standards

AJAX is based on the following web standards:

* JavaScript
* XML
* HTML
* CSS

The web standards used in AJAX are well defined, and supported by all major browsers. AJAX applications are browser and platform independent.
AJAX is About Better Internet Applications

Web applications have many benefits over desktop applications; they can reach a larger audience, they are easier to install and support, and easier to develop.

However, Internet applications are not always as “rich” and user-friendly as traditional desktop applications.

With AJAX, Internet applications can be made richer and more user-friendly.
You Can Start Using AJAX Today

There is nothing new to learn.

AJAX is based on existing standards. These standards have been used by most developers for several years.

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