AJAX
February 25, 2010 Leave a Comment
AJAX (Asynchronous JavaScript and XML)
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 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.
Try to create a XMLHttpRequest object:
xmlhttp=new XMLHttpRequest()
If not (if IE5 or IE6) create an ActiveXObject:
xmlhttp=new ActiveXObject(“Microsoft.XMLHTTP”)
Open the request object:
xmlhttp.open(“GET”,url,false)
Send your request to your server:
xmlhttp.send(null)
Update your page with the response from the server:
document.getElementById(‘test’).innerHTML=xmlhttp.responseText
Note: The code above can be used every time you need to create an XMLHttpRequest object, so just copy and paste it whenever you need it.
In the next chapter you will learn more about the XMLHttpRequest.
All Together Now
<html>
<head>
<script type=”text/javascript”>
function loadXMLDoc(url)
{
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject(“Microsoft.XMLHTTP”);
}
xmlhttp.open(“GET”,url,false);
xmlhttp.send(null);
document.getElementById(‘test’).innerHTML=xmlhttp.responseText;
}
</script>
</head>
<body>
<div id=”test”>
<h2>Click to let AJAX change this text</h2>
</div>
<button type=”button” onclick=”loadXMLDoc(‘test1.txt’)”>Click Me</button>
<button type=”button” onclick=”loadXMLDoc(‘test2.txt’)”>Click Me</button>
</body>
</html>
