Get the unique errors reported from ESLint by using custom formatters

unique-eslint-rule-formatter.js

module.exports = (results) => {
  const byRuleId = results.reduce((map, current) => {
    current.messages.forEach(({ ruleId, line, column }) => {
      if (!map[ruleId]) {
        map[ruleId] = [];
      }

      const occurrence = `${current.filePath}:${line}:${column}`;
      map[ruleId].push(occurrence);
    });
    return map;
  }, {});

  return Object.entries(byRuleId)
    .map(
      ([ruleId, occurrences]) =>
        `${ruleId} (total: ${occurrences.length})\n${occurrences.join("\n")}`
    )
    .join("\n--------------------------------------------\n");
};