Ajax for dummies, and not only.

Ajax
For dummies and not only…
Author: Alexios Tzanetopoulos - Developer

So…. What is Ajax?
 Ajax stands for: Asynchronous JavaScript and XML
 It is a set of techniques for creating highly interactive web sites and web
applications.
Examples?
http://www.aia.gr/traveler/flight-info/rtfi/
http://peteranswers.com/

Main idea
 The idea is to make what’s on the Web appear to be local by giving you a
rich user experience, offering you features that usually only appear in
desktop applications.

Is Ajax a technology?
Ajax is NOT a technology. It’s a combination of several technologies:
 standards-based presentation using XHTML and CSS;
 dynamic display, interaction using the Document Object Model (DOM);
 data interchange and manipulation using XML and JSON;
 asynchronous data retrieval using XMLHttpRequest object;
 and JavaScript binding everything together.

A little bit of History
 Microsoft Outlook Web Access team implemented Ajax in 1998
 Google maps and Gmail used it in 2005
 James Garret wrote an article combining the techniques that google used
and that’s how the term Ajax was coined (2005)
 W3C released the first draft specification for the XMLHttpRequest object in
an attempt to create an official web standard in 2006

Hands on code…
 HTML - CSS
<H1>An Ajax example</H1>
<form>
<input type = "button" value = "Fetch the
message“ onclick = "getData('data.php',
'targetDiv')">
</form>
<div id="targetDiv">
<p>The fetched message will appear
here.</p>
</div>

Hands on code… continued
 Javascript – XmlHttpRequest – DOM Manipulation
<script language = "javascript">
var XMLHttpRequestObject = false;
if (window.XMLHttpRequest) XMLHttpRequestObject = new XMLHttpRequest();
else if (window.ActiveXObject) {
XMLHttpRequestObject = new
ActiveXObject("Microsoft.XMLHTTP");}
function getData(dataSource, divID){
if(XMLHttpRequestObject) {
var obj = document.getElementById(divID);
XMLHttpRequestObject.open("GET", dataSource);
XMLHttpRequestObject.onreadystatechange = function(){
if (XMLHttpRequestObject.readyState == 4 && XMLHttpRequestObject.status == 200)
obj.innerHTML = XMLHttpRequestObject.responseText;
XMLHttpRequestObject.send(null);
}
}
</script>

Hands on code… continued
 PHP
<?php
echo 'This text comes to you thanks to PHP.';
?>

Result?
Don’t believe it? Click here!

Ready states and status codes
Ready states
 0 Uninitialized
 1 Loading
 2 Loaded
 3 Interactive
 4 Complete

Ready states and status codes
Status codes
 1xx Informational
 2xx Successful
 3xx Redirection
 4xx Client error
 5xx Server error
Famous examples
 200 OK
 201 Created
 400 Bad Request
 401 Unauthorized
 403 Forbidden
 404 Not Found

Possibilities
 That was plain text answer from the server. It could also be a xml or json
object
 Connection with a database
 Not only Get data but also Post data

Usages
 Web forms (password strength, autocomplete searches e.t.c.)
 On-page notifications (like facebook)
 On-site Instant Messaging (every chat uses ajax)
 Collaborative tools (many people working on the same doc)
 External widgets
 and many many many many more…

XML Format
<CATALOG>
<CD>
<TITLE>Empire Burlesque</TITLE>
<ARTIST>Bob Dylan</ARTIST>
<COUNTRY>USA</COUNTRY>
<COMPANY>Columbia</COMPANY>
<PRICE>10.90</PRICE>
<YEAR>1985</YEAR>
</CD>
….

XML Parsing
x=xmlhttp.responseXML.documentElement.getElementsByTagName("CD");
for (i=0;i<x.length;i++){
xx=x[i].getElementsByTagName("TITLE");{
txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";
}
xx=x[i].getElementsByTagName("ARTIST");
{
txt=txt + "<td>" + xx[0].firstChild.nodeValue + "</td>";
}
txt=txt + "</tr>";
}

Drawbacks
 Bookmarking a page
 Going back on a previous page
 Difficult for a web crawler to index a page
 Now every browser support javascript and XHR
 Difficult for screen readers

What About jQuery and AJAX?
 Writing regular AJAX code can be a bit tricky
 Different browsers have different syntax for AJAX implementation
 This means that you will have to write extra code to test for different
browsers
 The jQuery team has taken care of this for us
 We can write AJAX functionality with only one single line of code

jQuery load() Method
The jQuery load() method is a simple, but powerful AJAX method. It loads data
from a server and puts the returned data into the selected element.
$(selector).load(URL,data,callback);
 The required URL parameter specifies the URL you wish to load.
 The optional data parameter specifies a set of querystring key/value pairs
to send along with the request.
 The optional callback parameter is the name of a function to be executed
after the load() method is completed.

jQuery load() Method Ex.
jQuery
$("button").click(function(){
$("#div1").load("demo_test.txt",function(responseTxt,statusTxt,xhr){
if(statusTxt=="success")
alert("External content loaded successfully!");
if(statusTxt=="error")
alert("Error: "+xhr.status+": "+xhr.statusText);
});
});
demo_test.txt
<h2>jQuery and AJAX is FUN!!!</h2>
<p id="p1">This is some text in a paragraph.</p>

jQuery $.get() Method
The $.get() method requests data from the server with an HTTP GET request.
$.get(URL,callback);
 The required URL parameter specifies the URL you wish to request.
if the request succeeds.

jQuery $.get() Method Ex.
jQuery
$.get("demo_test.php",function(data,status){
alert("Data: " + data + "nStatus: " + status);
});
});
demo_test.php
<?php
echo 'This text comes to you thanks to PHP.';
?>

jQuery $.post() Method
The $.get() method requests data from the server with an HTTP POST request.
$.post(URL,data,callback);
 The required URL parameter specifies the URL you wish to request.
 The optional data parameter specifies some data to send along with the
request.
if the request succeeds.

jQuery $.post() Method Ex.
jQuery
$.post("demo_test_post.asp",
{
name:"Donald Duck",
city:"Duckburg"
},
function(data,status){
alert("Data: " + data + "nStatus: " + status);
});
});
demo_test.asp
<%
dim fname,city
fname=Request.Form("name")
city=Request.Form("city")
Response.Write("Dear " & fname & ". ")
Response.Write("Hope you live well in " & city & ".")
%>

HTTP GET vs HTTP POST
GET POST
BACK button/Reload Harmless
Data will be re-submitted (the browser
should alert the user that the data are
about to be re-submitted)
Bookmarked Can be bookmarked Cannot be bookmarked
Cached Can be cached Not cached
History Parameters remain in browser history
Parameters are not saved in browser
history
Restrictions on data length
Yes, when sending data, the GET method
adds the data to the URL; and the length
of a URL is limited (maximum URL length is
2048 characters)
No restrictions
Restrictions on data type Only ASCII characters allowed No restrictions. Binary data is also allowed
Security
GET is less secure compared to POST
because data sent is part of the URL
Never use GET when sending passwords or
other sensitive information!
POST is a little safer than GET because the
parameters are not stored in browser
history or in web server logs
Visibility Data is visible to everyone in the URL Data is not displayed in the URL

Too easy for you?
Take a look at reverse-ajax, a.k.a. Comet.
A Web server pushes data to a browser, without the browser explicitly
requesting it.
Good luck with it…

Like it?
Kris Hadlock – Ajax for Web Application Developers
http://www.w3schools.com/jquery/
http://en.wikipedia.org/wiki/Ajax_%28programming%29
http://thesharad.files.wordpress.com/2010/10/ajax-a-beginners-guide.pdf
Bibliography

Ajax for dummies, and not only.

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