webpack.config.js

const path = require('path');
const env = require('yargs').argv.env; // use --env with webpack 2
const pkg = require('./package.json');

const libraryName = pkg.name;

let outputFile, mode;

if (env === 'build') {
    mode = 'production';
    outputFile = `index.js`;
} else {
    mode = 'development';
    outputFile = `${libraryName}.js`;
}

const config = {
    mode,
    entry: __dirname + '/src/build.js',
    output: {
        path: __dirname + '/',
        filename: outputFile,
        library: libraryName,
        libraryTarget: 'umd',
        umdNamedDefine: true,
        globalObject: 'this'
    },
    module: {
        rules: [
            {
                test: /\.js$/,
                exclude: /node_modules/,
                loader: 'babel-loader'
            },
            {
                test: /\.jsx$/,
                exclude: /node_modules/,
                loader: 'babel-loader',
                query: {
                    presets: [
                        '@babel/env',
                        '@babel/preset-react'
                    ]
                }
            },
            {
                test: /\.css$/,
                exclude: /node_modules/,
                use: ['style-loader', 'css-loader']
            }
        ]
    },
    resolve: {
        modules: [path.resolve('./node_modules'), path.resolve('./src')],
        extensions: ['.json', '.js', '.jsx', '.css']
    }
};
module.exports = config;