markdown_heading_capitalization.js

// This file is used to trigger the custom rule that checks if all markdown headings (words longer than 4 characters) are written in the title case. To run this check, you must include the check in the markdownlint command.
// For example, if you want to run the check on the `docs` folder, run the following command: `markdownlint -r ./markdown_heading_capitalization.js docs/`.
module.exports = [
  {
    names: ['custom/capitalize-headings'],
    description: 'Heading words longer than 4 characters should be capitalized',
    tags: ['formatting'],
    function: function rule(params, onError) {
      params.tokens
        .filter(function filterToken(token) {
          return token.type === 'heading_open';
        })
        .forEach(function forToken(heading) {
          var headingTokenContent = heading.line.trim();
          var wordsInHeading = headingTokenContent.split(' ');

          for (var i = 0; i < wordsInHeading.length; i++) {
            if (
              wordsInHeading[i].length > 4 &&
              wordsInHeading[i] &&
              wordsInHeading[i].charAt(0) !==
                wordsInHeading[i].charAt(0).toUpperCase()
            ) {
              var capitalizedWord =
                wordsInHeading[i].charAt(0).toUpperCase() +
                wordsInHeading[i].slice(1);
              var detailMessage =
                'Change ' +
                "'" +
                wordsInHeading[i] +
                "'" +
                ' to ' +
                "'" +
                capitalizedWord +
                "'";

              onError({
                lineNumber: heading.lineNumber,
                detail: detailMessage,
                context: headingTokenContent, // Show the whole heading as context
                range: [
                  headingTokenContent.indexOf(wordsInHeading[i]),
                  wordsInHeading[i].length,
                ], // Underline the word which needs a change
              });
            }
          }
        });
    },
  },
];