Get the list of files inside a directory tree

directory-list.js

const fs = require('fs');
const path = require('path');

/**
 * Traversing a directory tree and get a list of the files inside it.
 * 
 * @param {string} dir 
 * Directory path
 * 
 * @return {string[]} 
 * Returns an array of file paths
 */
function getDirectoryFilesList(dir) {
  return fs.readdirSync(dir)
    .reduce((files, file) => {
      const filePath = path.join(dir, file);
      const stats = fs.statSync(filePath);
      return stats.isDirectory() ?
        files.concat(getDirectoryFilesList(filePath)) : files.concat(filePath);
    }, []);
}