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Detect Critical CSS
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset=utf-8 /> | |
| <title>JS Bin</title> | |
| </head> | |
| <body> | |
| <h2>Original CSS</h2> | |
| <style style="display: block; white-space: pre; font-family: monospace"> | |
| h2 { margin:0; } | |
| ol { color:red; } | |
| li { color:blue; background-color: red; } | |
| li:hover { color:purple; background-color: red; } | |
| li:first-child { color:green; background-color: yellow; } | |
| @media (max-width:512px) { | |
| li:first-child { color: cyan; background-color: lime; } | |
| } | |
| li:last-child { color:pink; background-color: blue; } | |
| </style> | |
| <h2>Critical CSS</h2> | |
| <pre id=output></pre> | |
| <p>Note the last-child is not in the output because it is not visible (unless you have a huge monitor, in which case, shame on you, shrink your window).</p> | |
| <ol> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| <li>TEST</li> | |
| </ol> | |
| </body> | |
| </html> |
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| // noprotect | |
| 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(); | |
| }; | |
| window.onload = function() { | |
| var cp = new CSSCriticalPath(window, document); | |
| var css = cp.generateCSS(); | |
| output.innerText = css; | |
| }; |
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