Chris Barr

Finding Unused CSS Rules

Wednesday, March 04, 2009

The other day I ran across a very useful article about the $$ selector in Firebug for Javascript and how to use it to loop through your stylesheets to find unused CSS styles. Very cool. The original code snippet would output everything to the firebug console, which I found to be useless on larger sites because I would hit Firebug's limit too often.

I modified it a bit to output the CSS to the actual site instead inside a styled element. So to use this on your own site, just copy and paste the code below into Firebug's console and hit run.

//Create a styled place to output styles to
var output = document.createElement('pre');
output.setAttribute("id","unusedCSSstyles");
output.setAttribute("style","height:95%; overflow:auto; text-align:left; background:#000000; border:2px outset #00CC33; color:#00CC33; opacity:0.9; padding:3px; position:fixed !important; left:5px; top:20px; width:95%; z-index:9998; font-size:12px;");

//create a styled close button
var closeBtn = document.createElement('a');
closeBtn.setAttribute("id","cssCloseBtn");
closeBtn.setAttribute("href","#");
closeBtn.setAttribute("onclick","document.body.removeChild(document.getElementById('unusedCSSstyles')); document.body.removeChild(document.getElementById('cssCloseBtn')); return false;");
closeBtn.setAttribute("style","position:fixed !important; left:2; top:0; z-index:9999; color:red; font-size:16px; padding:3px 20px; background-color:#000000; border:1px solid #FFF;");
closeBtn.innerHTML="close";

//add button and output element to body
document.body.appendChild(closeBtn);
document.body.appendChild(output);

//Find each stylesheet
for(var i = 0; i < document.styleSheets.length; i++) {
//write the filename to output element
output.innerHTML+="<br /><h3>"+document.styleSheets[i].href+"</h3>";
//find CSS rules
  for (var j = 0; j < document.styleSheets[i].cssRules.length; j++) {
    s = document.styleSheets[i].cssRules[j].selectorText;
    //write unused CSS rules to output element
    if ($$(s).length === 0) output.innerHTML+="<strong>["+j+"]</strong> "+s+"<br />";
  }
}

Do note that this has a few limitations:

• It cannot find stylesheets from another domain or subdomains
• It cannot find inline styles or the <style> tags anywhere
• It will not work on sites that use Mootools since it also uses the $$ selector. (this site does, so don't try it here!)

If you're really serious about finding what CSS styles you haven't used on your site, you might want to check out a Firefox plugin called Dust Me Selectors