critical css typo3 extension

This extension automatically detects and inlines critical css definitions.

how it works

The implementation of this extension does not use a browser to check a specific viewport size. Instead, it uses a marker that you can place anywhere on your site. The example TypoScript places it after the second tt_content element.

This extension will then use sophisticated regular expressions to create a statistic of what elements/attributes/classes/ids are used up until the marker. Then all css files are parsed using sabberworm/php-css-parser and all css selectors are matched against and reduced by the statistic created earlier.

This entire process is quiet fast even against huge frameworks like bootstrap and results in just 2-3 kb of inline css.

things you should know

• If the "below the fold" marker isn't present the extension will do nothing
• The inlined css is just a good guess of what you'll need. There is no browser selector matching at work. It guesses quiet good though...
• All animations/transitions as well as hover/focus effects are removed from the inline css since they aren't really important for the (hopefully at most) 1 second you'll have to wait until you get the real css
• external stylesheets are also downloaded and inlined (TODO create a good way to create exceptions)
• google fonts is currently a hardcoded exception from inlining since they deliver different fonts via user agent

when should i consider using this extension (or alternatives, i'm not judging)

• This should be one of the last optimizations you do
• Make sure there is nothing but css blocking the first paint or else this optimization is useless
• Make sure that your site isn't delivered via php since that will probably be the biggest performance improvement you can do. I recommend lochmueller/staticfilecache since it has no platform dependencies and is very transparent. But other strategies are fine too.

contributing

running the tests

The easiest way to run the test suite is by having docker installed and using the following commands:

• composer db:start which starts a docker image for a mysql database. This is required for functional tests.
• composer test runs unit and functional test suites. You can run them separately by using test:unit or test:functional. You can also pass filters using composer test:unit -- --filter External.
• composer db:stop will stop and remove the database again.

You can of course run them without docker if you have a database locally but then you'll have to compose your tests commands manually ;)