webpack.config.js

module.exports = {
    entry: './js/app.js',
    output: {
        path: './build',
        filename: 'bundle.js'
    },

    module: {
            loaders: [
                {
                    test: /\.js$/,
                    exclude: /node_modules/,
                    loader: 'babel-loader',
                    query: {
                     presets: ['es2015']
                    }
                }
             ]
     }
};