webpack.config.js

const path = require('path');
const ExtractTextPlugin = require('extract-text-webpack-plugin');

module.exports=(env)=> {
    console.log('env',env);
    const isProduction = env === 'production';
    const cssExtract =new ExtractTextPlugin('styles.css');
    return {
    entry : './src/app.js',
    output : {
        path : path.join(__dirname,'public'),
        filename : "bundle.js"
    },
    module : {
        rules : [{
            loader : 'babel-loader',
            test : /\.js$/,
            exclude : /node_modules/
        },
        {
            test: /\.(pdf|jpg|png|gif|svg|ico)$/,
            use: [
                {
                    loader: 'url-loader'
                },
            ]
        },
        {
            test : /\.s?css$/,
            use : cssExtract.extract({
                use : [
                    {
                        loader: 'css-loader',
                        options: {
                          sourceMap: true
                        }
                      },
                      {
                        loader: 'sass-loader',
                        options: {
                          sourceMap: true
                        }
                      }
                ]
            })
        }
    ]
    },
    plugins : [
        cssExtract
    ],
    devtool : isProduction? 'source-map' : 'inline-source-map',
    devServer : {
        contentBase : path.join(__dirname,'public')
    }
};

}