isSameOrigin

fiddle.html

Page url: <span id="location"></span>
<div>
<span class="url">http://fiddle.jshell.net</span> <span>true</span></div>
<div><span class="url">http://fiddle.jshell.net:80</span> <span>true</span></div>
<div><span class="url">//fiddle.jshell.net</span> <span>true</span></div>
<div><span class="url">//fiddle.jshell.net:80</span> <span>true</span></div>
<div><span class="url">http://fiddle.jshell.net:81</span> <span>false</span></div>
<div><span class="url">https://fiddle.jshell.net</span> <span>false</span></div>

fiddle.js

function isSameOrigin (url) {
	with (isSameOrigin.a || (isSameOrigin.a = document.createElement('a')))
		return href = url, host = host, !href.indexOf(/^.*?\w\//.exec(location)[0])
}
jQuery( function ( $ ) {
    $( '#location' ).html(
                    '<br>&nbsp;href: ' + location.href +
                    '<br>&nbsp;host: ' + location.host +
                    '<br>&nbsp;port: ' + location.port
    );
    $( '.url' ).each( function () {
        var self  = $( this )
            , log = self.next();
        self.css( 'color', 
            log.text()
            ==
            isSameOrigin( 
                self.text()
            ) + '' 
            ? 'green' : 'red'
        );
        log.html( 
            '<br>&nbsp;href: ' + isSameOrigin.a.href +
            '<br>&nbsp;host: ' + isSameOrigin.a.host +
            '<br>&nbsp;port: ' + isSameOrigin.a.port
        );
    } );
} );

fiddle.manifest

name: isSameOrigin tests
description: Test page to check a 140 bytes cross browser isSameOrigin function
# See: http://jsfiddle.net/gh/gist/jquery/1.7/2926596/