Use Webpack 2 to build JS and SASS files/bundles easily.

package.json

{
  "name": "frontend",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "autoprefixer": "^7.1.4",
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-preset-env": "^1.6.0",
    "babel-preset-react": "^6.24.1",
    "css-loader": "^0.28.7",
    "extract-text-webpack-plugin": "^3.0.0",
    "postcss-loader": "^2.0.6",
    "postcss-scss": "^1.0.2",
    "precss": "^2.0.0",
    "react": "^15.6.1",
    "react-dom": "^15.6.1",
    "webpack": "^3.6.0"
  }
}

postcss.config.js

module.exports = {
    parser: 'postcss-scss',
    plugins: [
        require('precss'),
        require('autoprefixer')
    ]
}

postcss.webpack.config.js

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


// JS Config
// ---------
const jsconfig = {
    entry: {
        channels: './src/pages/channels.js',
    },
    output: {
        path: path.join(__dirname, 'public', 'js'),
        filename: '[name].js'
    },
    module: {
        rules: [
            {
                test: /\.jsx?$/,
                exclude: /node_modules/,
                use: {
                    loader: 'babel-loader',
                    options: {
                        presets: ['env', 'react']
                    }
                }
            }
        ]
    },
    plugins: [
        new webpack.optimize.CommonsChunkPlugin({
            name: 'vendor'
        })
    ]
};


// CSS Config
// ----------
const cssconfig = {
    entry: {
        styles: './src/styles.css',
    },
    output: {
        path: path.join(__dirname, 'public', 'css'),
        filename: '[name].css'
    },
    module: {
        rules: [
            {
                test: /\.css$/,
                use: ExtractTextPlugin.extract({
                    use: [
                        {
                            loader: 'css-loader',
                            options: {
                                importLoaders: 1
                            }
                        },
                        'postcss-loader'
                    ]
                })
            }
        ]
    },
    plugins: [
        new ExtractTextPlugin('styles.css')
    ]
};


module.exports = [jsconfig, cssconfig];

webpack.config.js

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


// Note:
// ------
// We are using Webpack's "multi-compiler" feature to specify multiple config objects 
// to export. This is key to making this work easily as it allows us to isolate
// options relating to JS transpiling/bundeling from what is done for Sass files. 

// When using the sass-loader, one must also use the css-loader (first) to ensure that 
// css is translated correctly.

// Sass is compiled using a combination of css-loader, sass-loader + extract-text-webpack-plugin
// ------


// Javascript Config
// -----------------
const jsConfig = {
    entry: {
        website: './apps/Website/static/js/website.js',
        app: './apps/Backend/static/js/app.js',
    },
    output: {
        path: path.resolve(__dirname, 'public/js'),
        filename: '[name]-bundle.js'
    },
    module: {
        rules: [
            {
                test: /\.js$/,
                exclude: /(node_modules|bower_components)/,
                use: {
                    loader: 'babel-loader',
                    options: {
                        presets: ['env']
                    }
                }
            }
        ]
    }
};



// Sass Config
// -----------
const filename = '[name].css';
const sassConfig = {
    entry: {
        website: './apps/Website/static/sass/website.scss',
        backend: './apps/Backend/static/sass/backend.scss',
    },
    output: {
        path: path.resolve(__dirname, 'public/css'),
        filename: filename,
    },
    module: {
        rules: [
            {
                test: /\.scss$/,
                use: ExtractTextPlugin.extract({
                    use: ['css-loader', 'sass-loader']
                })
            }
        ]
    },
    plugins: [
        new ExtractTextPlugin(filename),
    ]
};


module.exports = [jsConfig, sassConfig];