Wednesday, November 28, 2012

Greasemonkey to rescue!

Greasemonkey is an add-on to Firefox that seems to prove to be really useful, so I wanted to give it a spin.

Basically, what it does is to modify webpages on-the-fly as you load them - using JavaScript. Many times I guess people use it to get rid of nasty ads and so forth. There are plenty of other add-ons able to do that - like removing a specific element each time, which doesn't require any coding. What fun is that?

Nonetheless, my first Greasemonkey-script does just that - removes an ad. But for the site in question - www.di.se (all in Swedish) - it isn't as easy as removing an element. The site is divided into 3 rows using a frameset that looks like this:

 
<frameset frameborder="no" framespacing="0" rows="0,210,*">
<frame class="noprint" frameborder="no" framespacing="0" name="historyFrame" noresize="" scrolling="no" src=""></frame>
<frame class="noprint" frameborder="no" framespacing="0" name="headerFrame" noresize="" scrolling="no" src=""></frame>
<frame class="" frameborder="no" framespacing="0" name="contentFrame" noresize="" scrolling="auto" src=""></frame>
</frameset>
As you maybe can tell, removing the second frame (which contains the 210px ad) doesn't cut it, because the third frame (content) will now take it's place.

This is where Greasemonkey comes to rescue! Creating the following script tells Greasemonkey to change to rows-attribute of the frameset to hide the ad frame, allowing the content frame to use all available space:

// ==UserScript==

// @name          Clean up di.se
// @namespace     http://www.technowobble.com
// @description   Removes the top add from www.di.se
// @include     http://www.di.se/
// @grant       none
// ==/UserScript==

var frameset = document.getElementsByTagName('frameset');

if (frameset[0]) {
 frameset[0].rows="0,0,*";
}
It will only be applied to http://www.di.se/ (notice the trailing slash which seems to be required) and I will never have to see the ad again. Sweet. But what more can you do with it? Anything, from removing ads, changing look & feel etc, to do automatic user interface testing or exploiting vulnerabilities, I guess?