{
  "plugins": {
    "metalsmith-babel": {
      "presets": ["@babel/preset-env"]
    }
  }
}

const Metalsmith = require('metalsmith');
const babel = require('metalsmith-babel');

const babelOptions = {
  presets: ['env']
};

new Metalsmith('./source')
.use(babel(babelOptions))
.build((err, files) => {
  if (err) {
    throw err;
  }

  console.log('Completed.');
});