“Print” media type defines the stylesheet rules for when the user tries to print the page, and the browser will load such stylesheet without delaying page rendering. Inlining extracted styles in the of the HTML document eliminates the need to make an additional request to fetch these styles and speeds up rendering. Shipping the CSS in a JavaScript file will cause it to be parsed and evaluated slowly.Ĭritical CSS is a technique that extracts and inlines the CSS for above-the-fold content. The secret to fast CSS-in-JS is inlining the CSS into the page or extracting it to an external CSS file. Here’s where using CSS-in-JS is a significant advantage: the styles rendered within each component is required CSS only. UnusedCSS and Purif圜SS are popular tools that can help pinpoint unnecessary styles, but we should pair them with careful visual regression testing. We have to carefully audit the entire site, in all possible states, on all possible devices (to cover media queries) and execute all JavaScript functionality that might be altering styles. Removing unused CSS is often manual work. The same issue appears in larger codebases that grow over a long time. When using CSS frameworks, it’s relatively common to end up with unused CSS (unless we only include the components we need).
Terser is a popular JavaScript compression tool and if you use webpack, v4 includes a plugin to create minified build files. The output is a smaller but perfectly valid code file that the browser can parse and that will save you some bytes. Minification is the process of removing whitespace and any code that is not necessary.
There’s also Brotli which can provide even better compression results, though it’s not as supported as Gzip. The most widely used compression format for server and client interactions is Gzip. Watch the size of CSS Compress and minify CSSĮstablishing a connection to download an external stylesheet inevitably causes latency, but you can speed up the download by minimising the total bytes transferred over the network.Ĭompressing files can significantly improve speed, and many hosting platforms and CDNs encode assets with compression by default (or you can configure them easily). To avoid blocking parsing, deliver the CSS as soon as possible and arrange your resources in optimal order. Parser blocking CSS: how CSS can block HTML parsing.
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