@mapbox/postcss-html-filter

postcss-html-filter

Filter CSS through HTML, removing selectors that do not apply to the HTML.

Parses HTML with Cheerio — using its jQuery-like selector queries — to determine which selectors in the CSS correspond to actual elements on the page. Removes selectors that have no corresponding elements, rules that have no corresponding selectors, at-rules containing no corresponding rules, etc.

Also, for good measure, runs the CSS through postcss-discard-unused, which removes unused @counter-style, @keyframes, and @font-face at-rules.

Example

const postcss = require('postcss');
const postcssHtmlFilter = require('postcss-html-filter');
const fs = require('fs');

const myHtml = fs.readFileSync('path/to/some.html', 'utf8');
postcss()
  .use(postcssHtmlFilter({ html: myHtml })
  .then(result => { /* ... */ });

Options

html

The HTML that you will use to filter your CSS.

Is this like UnCSS?

Kind of. This is essentially a simplified version of what UnCSS does. Instead of using PhantomJS or jsdom to load the page, try to size things, download resources, etc., this module address the core problem of filtering out CSS that is not used in some HTML. This is a low-level module that could be used within other, higher-level projects (e.g. ones that download resources).

Another project that uses Cheerio to filter out unused CSS is css-razor. Another PostCSS plugin with similar aims is usedcss.

Caveats

• This does not resolve nested selectors (e.g. for SCSS and Less). If you want to give that a shot, feel free to try a PR. Maybe try postcss-resolve-nested-selector.

Development

The tests are very simple. In fact, there's just one Jest snapshot test at the moment, which provides 100% code coverage. We can add more to the CSS and HTML fixtures, as needed, to test other scenarios and code changes; and Jest handles the comparison and offers a nice legible read-out of what went wrong.

Changelog

0.2.0

• Start this log.