function mergeDirsSync(source, destination) {
  for (const sourceFileBaseName of fs.readdirSync(source)) {
    const sourceFileName = path.join(source, sourceFileBaseName);
    const targetFileName = path.join(destination, sourceFileBaseName);

    const sourceFile = fs.statSync(sourceFileName);
    if (sourceFile.isDirectory()) {
      fse.ensureDirSync(targetFileName);
      mergeDirsSync(sourceFileName, targetFileName);
    } else {
      fs.copyFileSync(sourceFileName, targetFileName);
    }
  }
}
cross-platform alternative to `rsync -ar`
@param {string} source
@param {string} destination