Last active
March 17, 2021 22:09
-
-
Save matt-bailey/602b40c77a5d3381ff26 to your computer and use it in GitHub Desktop.
A simple script (based on one by Google) for loading CSS files asynchronously and conditionally based on body tag classes
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| <html> | |
| <head> | |
| <!-- Inlined critical styles --> | |
| <style>.blue{color:blue;}</style> | |
| <!-- CSS loader --> | |
| <script> | |
| /* ========================================================================== | |
| Load CSS asynchronously and conditionally after initial painting | |
| ========================================================================== */ | |
| /** | |
| * Modified function based on: https://developers.google.com/speed/docs/insights/OptimizeCSSDelivery | |
| */ | |
| /* Settings */ | |
| // Pass in a string containing your body tag classes here | |
| // Your CMS will usually have a template function you can use for this purpose | |
| var bodyClasses = 'class-name-one misc-class awesome-class'; | |
| // Define the class names and CSS files to match up with them | |
| var pagetypeCssData = [ | |
| { | |
| test: '', // Leaving this blank will load the files below on every page | |
| files: ['file-one.min.css', 'file-two.min.css'] | |
| }, { | |
| test: 'class-name-one', | |
| files: ['file-three.min.css', 'file-four.min.css'] | |
| }, { | |
| test: 'class-name-two', | |
| files: ['file-five.min.css', 'file-six.min.css'] | |
| } | |
| ]; | |
| // You can reverse the array so the files are processed in reverse order if you wish | |
| // pagetypeCssData.reverse(); | |
| /* Function to test if (body tag classes) string contains some text */ | |
| function stringHasText(string, text) { | |
| if(string.indexOf(text) >= 0) { | |
| return true; | |
| } else { | |
| return false; | |
| } | |
| } | |
| var cb = function() { | |
| /* Function to set media type to all */ | |
| function setMedia(element) { | |
| setTimeout(function() { | |
| element.media = 'all'; | |
| }); | |
| } | |
| /* Loop through pagetypeCssData[] and process the results */ | |
| for (var prop in pagetypeCssData) { | |
| if (stringHasText(bodyClasses, pagetypeCssData[prop].test)) { | |
| for (var i = 0, l = pagetypeCssData[prop].files.length; i < l; i++) { | |
| var link = document.createElement('link'); | |
| link.rel = 'stylesheet'; | |
| link.href = '/path/to/css/directory/' + pagetypeCssData[prop].files[i]; | |
| // Set media type to something non-matching so it doesn't block the render | |
| // Reference: https://github.com/filamentgroup/loadCSS/blob/master/loadCSS.js | |
| link.media = 'only x'; | |
| var firstScriptTag = document.getElementsByTagName('script')[0]; | |
| // Insert CSS file before first script tag | |
| firstScriptTag.parentNode.insertBefore(link, firstScriptTag); | |
| // Set the media type back to all | |
| setMedia(link); | |
| } | |
| } | |
| } | |
| }; | |
| var raf = requestAnimationFrame || mozRequestAnimationFrame || webkitRequestAnimationFrame || msRequestAnimationFrame; | |
| if (raf) { | |
| raf(cb); | |
| } else { | |
| window.addEventListener('load', cb); | |
| } | |
| </script> | |
| </head> | |
| <body class="class-name-one misc-class awesome-class"> | |
| <div class="blue">Hello, world!</div> | |
| </body> | |
| </html> |
It has come to my attention that requestAnimationFrame is not supported by IE 9<, iOS 5<, and Android.
If you need to support these browsers/OSs you can easily fix it by using a polyfill. Here's a gist by Paul Irish for just that purpose.
indexOf is also ie9+ and your function can be written more cleanly...
function stringHasText(string, text) {
return string.indexOf(text) !== -1;
}
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
I wanted a way to be able to asynchronously and conditionally load CSS files based on 'pagetype', so I modified a script by Google, found here: https://developers.google.com/speed/docs/insights/OptimizeCSSDelivery