CriticalCSS Bookmarklet and Devtool Snippet.js

criticalcss-bookmarklet-devtool-snippet.js

(function() { 
  var CSSCriticalPath = function(w, d, opts) {
    var opt = opts || {};
    var css = {};
    var pushCSS = function(r) {
      if(!!css[r.selectorText] === false) css[r.selectorText] = {};
      var styles = r.style.cssText.split(/;(?![A-Za-z0-9])/);
      for(var i = 0; i < styles.length; i++) {
        if(!!styles[i] === false) continue;
        var pair = styles[i].split(": ");
        pair[0] = pair[0].trim(); 
        pair[1] = pair[1].trim();
        css[r.selectorText][pair[0]] = pair[1];
      }
    };
    
    var parseTree = function() { 
      // Get a list of all the elements in the view.
      var height = w.innerHeight;
      var walker = d.createTreeWalker(d, NodeFilter.SHOW_ELEMENT, function(node) { return NodeFilter.FILTER_ACCEPT; }, true);
  
      while(walker.nextNode()) {
        var node = walker.currentNode;
        var rect = node.getBoundingClientRect();
        if(rect.top < height || opt.scanFullPage) {
          var rules = w.getMatchedCSSRules(node);
          if(!!rules) {
            for(var r = 0; r < rules.length; r++) {
              pushCSS(rules[r]); 
            }
          }
        } 
      }
    };
   
    this.generateCSS = function() {
      var finalCSS = "";
      for(var k in css) {
        finalCSS += k + " { ";
        for(var j in css[k]) {
          finalCSS += j + ": " + css[k][j] + "; ";
        }
        finalCSS += "}\n";
      }
      
      return finalCSS;
    };
    
    parseTree();
  };


  var cp = new CSSCriticalPath(window, document);
  var css = cp.generateCSS();
  
  console.log(css);
})();

@CameronKnowlton I just tried https://github.com/DirkPersky/criticalcss on the NY Times site and it worked for me in Chrome Canary Version 75.0.3740.0 macOS 10.13.6. The generated critical CSS is displayed in the console in DevTools.

Just tried DirkPersky's bookmarklet. It works. Thanks!

Hello, Paul Kilan's code pops an error and DirkPerky's code does nothing. Anyone knows a working script to run on Chrome console to extract the critical css?

hi DirkPersky , I wasn't able to get your https://github.com/DirkPersky/criticalcss bookmarklet working in Chrome 72 Mac... should it be working? I tried it on several URLs, nothing happens (e.g. https://www.nytimes.com/ ). Thanks for your work on this.

Same issue here. Nothing happens.

On Windows 10 with Crome 83.0.... the Bookmarklet works.
Maybe update your Chrome.

@fisiculturista

Hi, I was sent here via the Autoptimize plugin FAQ. I have no clue how to use this to generate critical/above the fold CSS for the inline and defer css field of AO. Using another critical css generator I am getting the flash of unoptimized code (something like that). Could somebody please point me in the right direction of how to use this tool to extract (*the FAQ link points to this page)
Thanks!
Jon

@gatehealing you create a new bookmark, and copy all javascript code from my https://github.com/DirkPersky/criticalcss/blob/master/bookmark.js into that field like the screenshot =)

using it:
open the developer console, on you site and press the bookmark button in yout browser an wait for it ;)

Thanks DirkPersky! Please forgive my ignorance . . . what page am I bookmarking? This one (the one I am commenting on?)

@gatehealing Non of both! Only create a new bookmark, but instead of adding a url to it, copy the content of my javascript and paste it to the url =)

got it! Now what I see is not wrapped in <style></style> tags, and I believe I am supposed to put what is wrapped in those style tags in the AO inline and defer css box. I don't want to crash my site (which I have managed to do before on things like this), so I want to be sure I have extracted the correct code to put in that AO field....

FWIW I also made a version of the bookmarklet, and I even accounted for some cases where the cssRules or rules property threw an error on access.

I get Uncaught TypeError: w.getMatchedCSSRules is not a function , using Chrome

I get Uncaught TypeError: w.getMatchedCSSRules is not a function , using Chrome

My re-fashioning used a polyfill for that; getMatchedCSSRules was never standardized, and it was removed from Chrome starting with version 63.

I was able to get it working by replacing getMatchedCSSRules with the script below. However doesn't work if css is from a different domain.

 var getCSS = function(el) {
    var sheets = document.styleSheets, ret = [];
    el.matches = el.matches || el.webkitMatchesSelector || el.mozMatchesSelector 
        || el.msMatchesSelector || el.oMatchesSelector;
    for (var i in sheets) {
        var rules; 
      try {
        rules = sheets[i].rules; 
      } catch {
        console.log("Error reading rules: "); 
        try{
          rules = sheets[i].cssRules;
         
        } catch {
           console.log("Error reading cssRules: "); 
          
        }
         
      }
     
     ```

this library is probably the way to go: https://www.brothercake.com/site/resources/scripts/cssutilities/

Your example script was not complete, but I imagine the rest of the way you'd do it is to test the element against each rule to see whether it matches.