notes/node_modules/stylelint/docs/developer-guide/processors.md

Writing processors

Processors are functions that hook into stylelint's pipeline, modifying code on its way into stylelint and modifying results on their way out.

Processors can only be used with the CLI and the Node API, not with the PostCSS plugin.

Processor modules are functions that accept an options object and return an object with the following the functions, which hook into the processing of each file:

• code: A function that accepts two arguments, the file's code and the file's path, and returns a string for stylelint to lint.
• result: A function that accepts two arguments, the file's stylelint result object and the file's path, and either mutates the result object (returning nothing) or returns a new one.

// my-processor.js
module.exports = function(options) {
  return {
    code: function(input, filepath) {
      // ...
      return transformedCode;
    },
    result: function(stylelintResult, filepath) {
      // ...
      return transformedResult;
    }
  };
}

Processors can enable stylelint to lint the CSS within non-stylesheet files. For example, let's say you want to lint the CSS within <style> tags in HTML. If you just feed stylelint your HTML code, you'll run into problems, because PostCSS does not parse HTML. Instead, you can create a processor that does the following:

• In the code processor function, extract CSS from the <style> tags in the HTML code. Return a CSS string containing all that extracted CSS, which is what stylelint will inspect.
• Build a sourcemap while performing the extraction, so warning positions can be tailored to match the original source HTML.
• In the result processor function, modify the line/column position of each warning using your sourcemap.

Processor options must be JSON-friendly, because users will need to include them in .stylelintrc files.

Sharing processors

• Use the stylelint-processor keyword within your package.json.
• Once your processor is published, please send us a Pull Request to add your processor to the list.