webpack.dev.js

const webpack = require("webpack");
const path = require("path");
const webpackMerge = require("webpack-merge");

// common config
const common = require("./webpack.common");

// constants
const ENV = (process.env.NODE_ENV = process.env.ENV = "development");

module.exports = webpackMerge(common.config, {
  output: {
    filename: "[name].[hash:20].js"
  },
  module: {
    rules: [
      {
        test: /\.css$/,
        use: ["style-loader", "css-loader"],
        exclude: /node_modules/
      },
      {
        test: /\.scss$/,
        use: ["style-loader", "css-loader", "sass-loader"],
        exclude: /node_modules/
      }
    ]
  },
  plugins: [
    new webpack.DefinePlugin({
      "process.env": {
        ENV: JSON.stringify(ENV)
      }
    })
  ],
  devServer: {
    contentBase: path.resolve(__dirname, "../dist")
  }
});