Custom eslint formatter (reporter) making multiple reports for a single lint run

custom-lint-formatter.js

const fs = require('fs');

const fileFormatter = require('eslint/lib/cli-engine/formatters/html');
const outputFormatter = require('eslint/lib/cli-engine/formatters/stylish');

function formatter(results = [], data) {
  saveA11yReport(results, data);
  const output = outputFormatter(results, data);

  return output;
}

function saveA11yReport(results, data) {
  // a11y errors and warnings
  const a11yRelated = results
    .filter(r => r.messages.some(m => m.ruleId.startsWith('jsx-a11y/')))
    .map(r => {
      const messages = r.messages.filter(m => m.ruleId.startsWith('jsx-a11y/'));

      return {
        ...r,
        messages,
        errorCount: messages.filter(m => m.severity == 2).length,
        warningCount: messages.filter(m => m.severity == 1).length,
      };
    });

  const a11yHtml = fileFormatter(a11yRelated, data);

  fs.writeFileSync('./dist/a11y.report.html', a11yHtml, 'utf8');
}

module.exports = formatter;

Sample usage:

eslint -f ./custom-lint-formatter "./src/**/*.{js,jsx,ts,tsx}"

or in package.json

{
 "scripts": {
    "lint": "eslint -f ./custom-lint-formatter.js \"./src/**/*.{js,jsx,ts,tsx}\"",
  }
}