package.json

{
  "name": "bundle-all",
  "version": "1.0.0",
  "description": "",
  "main": "main.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.3",
    "babel-preset-es2015": "^6.24.1",
    "css-loader": "^0.28.10",
    "node-sass": "^4.7.2",
    "sass-loader": "^6.0.7",
    "copy-webpack-plugin": "^4.5.0",
    "extract-text-webpack-plugin": "^4.0.0-beta.0",
    "webpack": "^4.0.1",
    "webpack-glob": "^2.0.2"
  }
}

webpack.config.js

const glob = require("glob");
const CopyWebpackPlugin = require('copy-webpack-plugin');
const ExtractTextPlugin = require('extract-text-webpack-plugin');

const getFileLists = (...data) => {
    let ret = {};
    for( [i, obj] of Object.entries(data) ){
        let path = `${obj.base}${obj.src}`;
        pathList = glob.sync(path);
        for( [i, p] of Object.entries(pathList) ){
            let key = obj.dest+p.split('/').slice(-1)[0];
            if(typeof obj.ext != "undefined"){
                key = key.replace(obj.src.split('.').slice(-1)[0].trim(),obj.ext);
            }

            if(typeof ret[key] == "undefined"){
                ret[key] = [p];
            }else{
                ret[key].push(p);
            }
        }   
    }

    return ret;
}

const stylesheets = {
    base: './assets/src/scss/',
    src: '*.scss',
    dest:'./assets/build/css/',
    'ext': 'css'
};

const scripts = {
    base: './assets/src/js/',
    src: '*.js',
    dest:'/assets/build/js/'
};

let filesToTranspile = {};

filesToTranspile = getFileLists(scripts, stylesheets);
filesToTranspile['./assets/build/css/main.css'].push('./assets/src/css/style.css');

const mode = 'development';

module.exports = {
	mode: mode,
    entry: filesToTranspile,
    output: {
        path: __dirname,
        filename: '[name]'
    },
    
    watch: true,

    module: {
    	rules: [
    		{
    			test: /\.js$/,
    			exclude: /node_modules/,
    			loader: 'babel-loader',
    			options: {
    				presets: ['es2015']
    			}
    		},

            {
                test: /\.css$/,
                exclude: /node_modules/,
                use: ExtractTextPlugin.extract({
                    use: [
                        { loader: 'css-loader', options: {
                            minimize: ((mode=='production')?true:false) 
                        } },
                        { loader : 'sass-loader', options: {
                            sourceMap: true,
                            outputStyle: 'expanded',
                            minimize: ((mode=='production')?true:false) 
                        } }
                    ]
                })
            },
            {
                test: /\.scss$/,
                exclude: /node_modules/,
                use: ExtractTextPlugin.extract({
                    use: [
                        { loader: 'css-loader', options: {
                            minimize: ((mode=='production')?true:false) 
                        } },
                        { loader : 'sass-loader', options: {
                            sourceMap: true,
                            outputStyle: 'expanded',
                            minimize: ((mode=='production')?true:false) 
                        } }
                    ]
                })
            }
    	]
    },
    plugins: [
        new ExtractTextPlugin({
            filename: (getPath) => {
                let path = getPath('[name]').replace('js','css').replace('scss', 'css');             
                return path
            },
            allChunks: true,
        }),

        new CopyWebpackPlugin([
            { from: './assets/src/img/', to: './assets/build/img/' },
            { from: './assets/src/fonts/', to: './assets/build/fonts/' }
        ])
    ],
};