gulpfile.js

gulp.task('build:javascripts', function(cb) {
  webpack({
    entry: __dirname + '/app/frontend/javascripts/gifts.js',
    output: {
      path: __dirname + '/app/assets/javascripts',
      filename: 'gifts.js'
    },
    devtool: "#source-map",
    module: {
      loaders: [
        {
          test: /\.js$/,
          exlude: /node_modules/,
          loader: 'babel-loader'
        }
      ]
    }
  }, function(err, stats) {
    if(err) {
      throw new gutil.Plugin("webpack", err);
    }

    gutil.log("[webpack]", stats.toString());
    cb();
  });
});

.babelrc:

{
"presets": ["es2015", "react"]
}