About the Build Mode with Webpack

$ npx webpack --config webpack.config.js --mode=development

$ npx webpack --config webpack.config.js --mode=production

const webpack = require('webpack');

module.exports = (env, argv) => {
    return {
        // other directives...
        plugins: [
            new webpack.DefinePlugin({
                PRODUCTION: JSON.stringify(argv.mode === 'production'),
            }),
        ],
    }
};

if (PRODUCTION) {
    console.log("This is a production build.");
} else {
    console.log("This is a development build.");
}