Suppose you want to use your website to pull data from another website? This presentaion discusses CORS and how to build a simple application that allows you to achieve the objective.

1. Pulling data from another website
A presentation by Michael Russell

2. “client” site
“server” site

3.  Prevents a script running in the browser from calling
methods and resources offered by different websites
from the one that hosts the script

5.  An “application”—a script—on the client
 A small change to the .htaccess file on the server
 A “CORS-aware” browser

6. The Javascript
<joomla-root>/libraries/rnReader.js
var kQA_el = document.getElementById("kQA_RNotes");
kQA_el.style.display = 'none';
kQA_isHidden = false;
var kQA_el2 = document.getElementById("kQA_RTable");
kQA_el2.style.display = 'none';
kQA_isHidden2 = false;
function kQA_readTextfile(filename) {
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if(xhr.readyState === 4) {
if(xhr.status == 200) {
kQA_showContents(xhr.responseText, xhr);
}
}
}
xhr.open('GET', filename, true);
xhr.send();
}
function kQA_showContents(responseText) {
kQA_el.innerHTML = responseText.replace(/</g,"&lt;");
kQA_isHidden = !kQA_isHidden;
if (kQA_isHidden) {
kQA_el.style.display = '';
}
else {
kQA_el.style.display = 'none';
}
}
function kQA_hideShowTable() {
kQA_isHidden2 = !kQA_isHidden2;
if (kQA_isHidden2) {
kQA_el2.style.display = '';
}
else {
kQA_el2.style.display = 'none';
}
}

7.  The web-page
• Write a Joomla article (set your editor to “none” so that you
can use <script> elements)
<div id="kQA_technical">
<p class="blog">This is a simple demonstration of an application that
reads a text file from another website and displays the information
here on this page
<div class="releaseNotes">CHANGELOG <a name="changelog"><span
class="releaseNotes" title="Hide/display changelog"
onclick="kQA_readTextfile('http://www.site-b.com/textfile.txt');"> </span></a>
<pre id="kQA_RNotes">&nbsp;</pre>
</div>
</div>
<script type="text/javascript" src="libraries/rnReader.js"></script>

8.  To allow access from a single site, add the following
lines to the end of your .htaccess file:
# Trust AJAX read requests from site-a
#Header set Access-Control-Allow-Origin "http://www.site-a.com"
Header set Access-Control-Allow-Headers "origin, x-requested-with, content-type"
Header set Access-Control-Allow-Methods "PUT, GET, POST"
Header set Access-Control-Allow-Credentials true
 To allow access from any site:
# Trust AJAX read requests from any site
#Header set Access-Control-Allow-Origin “*"
Header set Access-Control-Allow-Headers "origin, x-requested-with, content-type"
Header set Access-Control-Allow-Methods "PUT, GET, POST"
Header set Access-Control-Allow-Credentials true

9.  Cross-origin resource sharing demonstration