husky pre-commit hook for handling ONLY staged files that will prevent commit if there are linting errors and auto-fix them

.huskyrc.js

/**
 * @see {@tutorial https://github.com/typicode/husky}
 * _Requires Node >= 10 and Git >= 2.13.0._
 */
module.exports = {
  hooks: {
    /**
     * @see {@tutorial https://stackoverflow.com/a/15656652/3942699}
     * 
     * ___only works with files staged in git___
     * because doing on the entire repo is overkill atm
     * 
     * if linting succeeds, proceed to committing the staged files.
     * if linting fails, prevent the commit from happening and fix the auto-fixable errors
     */
    'pre-commit': `
      stagedFiles=$(git diff --diff-filter=d --cached --name-only);
      if [ -n "$stagedFiles" ]; then # at least one file is staged
        {
          npx eslint $stagedFiles
        } || {
          npx eslint --fix $stagedFiles && exit 1
        }
      fi
    `,
  },
};

lint.ts

/**
 * performs linting (eslint) and formatting (prettier) on __staged files only__
 *
 * (probably as a pre-commit hook @see .huskyrc.js)
 */
export default async () => {
  const { default: chalk } = await import('chalk');

  const { read, run } = await import('./utils');

  const stagedFiles = (await read('git diff --diff-filter=d --cached --name-only'))
    .split('\n')
    .filter(Boolean);

  if (stagedFiles.length) {
    console.log(chalk.blueBright('\nLinting staged files with ESLint before committing...'));

    /** eslint only works with js and ts for now */
    const stagedFilesForEslint = stagedFiles.filter((f) => f.match(/\.(js|jsx|ts|tsx|vue|json)$/));
    const stagedFilesForEslintStr = stagedFilesForEslint.join(' ');

    /**
     * a reusable function for formatting with Prettier.
     * this function should be called after either:
     * - linting succeeds or
     * - linting fails and then lint --fix is attempted
     */
    const formatStagedFilesWithPrettier = async () => {
      try {
        console.log(
          chalk.blueBright('\nFormatting staged files with Prettier before committing...\n')
        );
        const stagedFilesStr = stagedFiles.join(' ');
        await read(`npx prettier --list-different ${stagedFilesStr}`);
        // nothing to format
      } catch (resultOfCheckingToSeeIfAnythingNeedsToBeFormatted) {
        const filesThatNeedToBeFormatted = (resultOfCheckingToSeeIfAnythingNeedsToBeFormatted.stdout as string)
          .split('\n')
          .filter(Boolean);

        if (filesThatNeedToBeFormatted.length) {
          try {
            await read(`npx prettier --write ${filesThatNeedToBeFormatted.join(' ')}`);
          } finally {
            const { default: path } = await import('path');
            console.log(chalk.redBright.bold('The following files needed formatting:'));
            const cwd = process.cwd();
            filesThatNeedToBeFormatted.forEach((f) =>
              console.log(chalk.underline(path.join(cwd, f)))
            );
            console.log();
            process.exit(1);
          }
        }
      }
    };

    try {
      stagedFilesForEslint.length && (await run(`npx eslint ${stagedFilesForEslintStr}`));
      await formatStagedFilesWithPrettier();
    } catch (lintingErr) {
      // there are linting problems, so:
      // 1. try to fix the linting problems with eslint --fix
      // 2. try to format the code with prettier --write
      // 3. prevent the commit from happening

      console.log(chalk.blueBright('Attempting to `--fix` problems...'));

      try {
        stagedFilesForEslint.length && (await run(`npx eslint --fix ${stagedFilesForEslintStr}`));
        await formatStagedFilesWithPrettier();
      } finally {
        process.exit(1);
      }
    }
  } else {
    console.log(chalk.blueBright('\nThere are no files staged in git to lint/format\n'));
  }
};

export const LINT_MESSAGE = 'Lint and format staged files';