webpack.config.js

const path = require('path');
const webpack = require('webpack');

module.exports = {
    entry: {
        app: './src/index.js',
        background: './src/background.js',
    },
    output: {
        // This copies each source entry into the extension dist folder named
        // after its entry config key.
        path: path.join(__dirname, 'extension/dist'),
        filename: '[name].js',
    },
    module: {
        rules: [
            {
                test: /\.m?js$/,
                exclude: /(node_modules|bower_components)/,
                use: {
                    loader: 'babel-loader',
                    options: {
                        presets: [
                            [
                                '@babel/preset-env',
                                {
                                    "targets": {
                                        "firefox": "69"
                                    }
                                }
                            ],
                            '@babel/preset-react']
                    }
                }
            },
            {
                test: /\.css$/,
                use: [
                    'style-loader',
                    'css-loader'
                ]
            },
            {
                test: /\.s[ac]ss$/i,
                use: [
                    // Creates `style` nodes from JS strings
                    'style-loader',
                    // Translates CSS into CommonJS
                    'css-loader',
                    // Compiles Sass to CSS
                    'sass-loader',
                ]
            },
            {
                test: /\.(ttf|eot|svg)(\?v=[0-9]\.[0-9]\.[0-9])?$/,
                loader: 'file-loader'
            }
        ],
    },
    resolve: {
        extensions: ['.js', '.jsx'],
        modules: [
            path.join(__dirname, 'src'),
            'node_modules'
        ]
    },
    plugins: [
        // Since some NodeJS modules expect to be running in Node, it is helpful
        // to set this environment var to avoid reference errors.
        new webpack.DefinePlugin({
            'process.env.NODE_ENV': JSON.stringify('production'),
        })
    ],
    // This will expose source map files so that errors will point to your
    // original source files instead of the transpiled files.
    devtool: 'sourcemap',
    //devtool: false,
    mode: 'development'
};