Regular Expression

Extracting domain name from URL.
Example:

URL: http://www3.braingia.org
Domain Name: braingia.org

JavaScript:

var myString = "http://www3.braingia.org";
var myRegex = /http:\/\/\w+\.(.*)/;
var results = myRegex.exec(myString);
alert(results[1]);

Regular Expression: 
/http:\/\/\w+\.(.*)/

The Idea:
What's inside of ( ) will be extracted. 
Here's how it works.

http: looks for http:
\/\/ looks for //
   Note that \(back slash) is an escape charactor
\w looks for any numaric charactor
+ makes it continue until it find non-numaric charactor
   Note that /w+ doesn't mean “w”! 
\. looks for . Now, it came up to the beginning of braingia.org
.* means match any character, and any and all of the previous charactors
And finally, ( ) extracts what parsed by .*

Posted below are the files just do that

HTML File (index.html)

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title></title>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <link rel ="stylesheet" type = "text/css" href = "style.css">
    <script type ="text/javascript" src ="extractDomain.js"></script>
  </head>
  <body>
    <div id="wrapper">
      <div id ="innerWrapper">
        <h2>JavaScript: Learning Regular Expression</h2>
        <div id="ex">
            <p>Using RegExp object, extract domain name from URL</p>
            <p>In this example, it extracts
                <span class = "hilight">braingia.org</span>
                from <span class ="hilight"> http:\\www.braingia.org</span>
            </p>
        </div>
      </div>
    </div>
  </body>
</html>

CSS File (style.css)

body {
  text-align:center;
  font-family:"arial",verdana,sans-serif;
  color: gray; 
  background-color: #f2f2f2;
}
#wrapper{
  margin: 0 auto;
  width: 900px;
  text-align: left;
  background: white;
}
#innerWrapper{
  margin-left: 20px;
}
#ex{
    color: gray;
}
.hilight{
    color: orangered;
}

JavaScript File (extractDomain.js)

var myString = "http://www3.braingia.org";
var myRegex = /http:\/\/\w+\.(.*)/;
var results = myRegex.exec(myString);
alert(results[1]);