webpack.config.js

const webpack = require('webpack');
const NODE_ENV = process.env.NODE_ENV || 'development';
const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
    mode: NODE_ENV,
    entry: './dashboard/index.js',
    output: {
        path: __dirname,
        filename: './dist/dashboard/build.js'
    },
    module: {
        rules: [
            {
                test: /.js?$/,
                use: [{
                    loader: 'babel-loader',
                    options: {
                        presets: ['@babel/preset-env'],
                        plugins: [
                            '@babel/plugin-transform-async-to-generator',
                            '@babel/plugin-proposal-object-rest-spread',
                            [
                                '@babel/plugin-transform-react-jsx', {
                                    'pragma': 'wp.element.createElement'
                                }
                            ]
                        ]
                    }
                },
                ],
                exclude: /node_modules/
            },
            {
                test: /\.(css|scss)$/,
                use: [{
                    loader: MiniCssExtractPlugin.loader
                },
                    'css-loader',
                {
                    loader: 'postcss-loader',
                    options: {
                        plugins: [
                            require('autoprefixer')
                        ]
                    }
                },
                    'sass-loader']
            }
        ]
    },
    plugins: [
        new webpack.DefinePlugin({
            'process.env.NODE_ENV': JSON.stringify(NODE_ENV)
        }),
        new MiniCssExtractPlugin({
            filename: './dist/dashboard/build.css'
        })
    ]
};