(function() {
var CSSCriticalPath = function(w, d) {
var css = {};
var pushCSS = function(r) {
// The last selector wins, so over-write
// merging existing css will happen here...
css[r.selectorText] = r.cssText;
};
var parseTree = function() {
// Get a list of all the elements in the view.
var height = w.innerHeight;
var walker = d.createTreeWalker(d.body, 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) {
// element is in the first scroll of the screen
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 += css[k] + "\n";
}
return finalCSS;
};
parseTree();
};
var cp = new CSSCriticalPath(window, document);
var css = cp.generateCSS();
console.log(css);
})();