webpack.config.js

var Encore = require('@symfony/webpack-encore');

Encore
    // the project directory where compiled assets will be stored
    .setOutputPath('docs/build')
    // the public path used by the web server to access the previous directory
    .setPublicPath('/build')
    .cleanupOutputBeforeBuild()
    .enableSourceMaps(!Encore.isProduction())
    // uncomment to create hashed filenames (e.g. app.abc123.css)
    // .enableVersioning(Encore.isProduction())

    // uncomment to define the assets of the project
    .addEntry('js/app', './assets/js/App.jsx')
    .addStyleEntry('css/app', './assets/scss/app.scss')

    .enableSassLoader()
    .enableReactPreset()

    // first, install any presets you want to use (e.g. yarn add babel-preset-es2017)
    // then, modify the default Babel configuration
    .configureBabel(function(babelConfig) {
        // add additional presets
        babelConfig.presets.push('es2017');

        // no plugins are added by default, but you can add some
        // babelConfig.plugins.push('styled-jsx/babel');
    })
;

module.exports = Encore.getWebpackConfig();