AJAX
Introduction
AJAX is a
developer's dream, because you can:
Update a web
page without reloading the page
Request data
from a server - after the page has loaded
Receive data
from a server - after the page has loaded
Send data to
a server - in the background
Examples in
Every Chapter
In every
chapter, you can edit the examples online, and click on a button to view the
result.
AJAX
Example
Let AJAX
change this text
Change
Content
»
AJAX
Example Explained
HTML Page
<!DOCTYPE
html>
<html>
<body>
<div
id="demo">
<h2>Let AJAX change this
text</h2>
<button type="button"
onclick="loadDoc()">Change Content</button>
</div>
</body>
</html>
The HTML
page contains a <div> section and a <button>.
The
<div> section is used to display information from a server.
The
<button> calls a function (if it is clicked).
The function
requests data from a web server and displays it:
Function
loadDoc()
function
loadDoc() {
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 &&
this.status == 200) {
document.getElementById("demo").innerHTML = this.responseText;
}
};
xhttp.open("GET",
"ajax_info.txt", true);
xhttp.send();
}
What
is AJAX?
AJAX =
Asynchronous JavaScript And XML.
AJAX is not
a programming language.
AJAX just
uses a combination of:
A browser
built-in XMLHttpRequest object (to request data from a web server)
JavaScript
and HTML DOM (to display or use the data)
AJAX is a
misleading name. AJAX applications might use XML to transport data, but it is
equally common to transport data as plain text or JSON text.
AJAX allows
web pages to be updated asynchronously by exchanging data with a web server
behind the scenes. This means that it is possible to update parts of a web
page, without reloading the whole page.
How AJAX
Works
1. An event
occurs in a web page (the page is loaded, a button is clicked)
2. An
XMLHttpRequest object is created by JavaScript
3. The
XMLHttpRequest object sends a request to a web server
4. The
server processes the request
5. The
server sends a response back to the web page
6. The
response is read by JavaScript
7. Proper
action (like page update) is performed by JavaScript
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