freeCodeCamp/packages/eslint-config/.lintstagedrc.js

import { ESLint } from 'eslint';

export const createLintStagedConfig = cwd => {
  // cwd has to be passed to ESLint or it defaults to process.cwd(), i.e. the root
  // of the monorepo.
  const cli = new ESLint({ cwd });
  return {
    '*.(mjs|js|ts|tsx)': async files => {
      const ignoredIds = await Promise.all(
        files.map(file => cli.isPathIgnored(file))
      );

      const lintableFiles = files.filter((_, i) => !ignoredIds[i]);
      const prettierCommand = [
        ...files.map(filename => `prettier --write '${filename}'`)
      ];

      // There should be at least one lintable file if we reach here, but if not,
      // just run prettier.
      return lintableFiles.length === 0
        ? prettierCommand
        : ['eslint --fix ' + lintableFiles.join(' '), ...prettierCommand];
    },
    '*.!(mjs|js|ts|tsx|css|md)': files =>
      files.map(filename => `prettier --write --ignore-unknown '${filename}'`),

    '*.css': files => [
      ...files.map(filename => `stylelint --fix '${filename}'`),
      ...files.map(filename => `prettier --write '${filename}'`)
    ]
  };
};