generate an index.js file as a commonjs style module

index-dot-js-maker.js

// usage: `node index-dot-js-maker.js <target directory>`

const Promise = require('bluebird');
const fs = Promise.promisifyAll(require('fs'));
const path = require('path');
const _ = require('lodash');

const cwd = process.cwd();
const maindir = path.resolve(cwd, process.argv[process.argv.length - 1]);


const indexFilenameMapper = filename => path.resolve(maindir, filename, 'index.js');
const fileExistsMapperAsync = filePath => fs.accessAsync(filePath, fs.constants.F_OK)
  .then(() => true)
  .catch(() => false);
const isJs = filename => filename.match(/^.*\.js$/);
const isSpec = filename => filename.match(/^.*\.spec\.js$/);
const isIndex = filename => filename.match(/index\.js/);


fs.readdirAsync(maindir)
  .then((filenames) => {
    const jsFiles = filenames
      .filter(filename => isJs(filename) && !isSpec(filename) && !isIndex(filename))
      .map(filename => filename.replace('.js', ''));

    const folderPromises = filenames
      .filter(filename => !isJs(filename))
      .map(filename => fileExistsMapperAsync(indexFilenameMapper(filename))
        .then(exists => exists && filename)
      );
    return Promise.filter(jsFiles.concat(folderPromises), val => val); // remove falsy values from "exists" check
  })
  .then((filesToIndex) => {
    const orderedFiles = filesToIndex.sort();
    const requireLines = orderedFiles
      .map(filename => `const ${_.camelCase(filename)} = require('./${filename}');`)
      .join('\n');
    const exportsLines = orderedFiles
      .map(filename => `  ${_.camelCase(filename)},`)
      .join('\n');
    const indexDotJsFile =
`${requireLines}

module.exports = {
${exportsLines}
};
`;
    fs.createWriteStream(path.resolve(maindir, 'index.js')).end(indexDotJsFile);
  });