npm install webpack -g

cd webpack4-babel-uglify
npm init -y
npm install webpack webpack-cli --save-dev

npm install babel-core babel-loader@7 babel-plugin-transform-runtime babel-preset-env --save-dev
npm install babel-polyfill babel-runtime --save

mkdir src

module.exports = {
 mode:'development',
 entry: {
 app: [
  "babel-polyfill", 
  "./src/index.js" //需要压缩的js，目前只支持单个文件一个一个压缩 = =！
 ],
 },
 output: {
 path: path.resolve(__dirname, 'dist'), //输出目录
 filename: 'index.js' //输出文件名称，建议与源文件同名
 },
 module: {
 rules: [{
  test: /\.js$/,
  exclude: /(node_modules)/,
  use: {
  loader: "babel-loader"
  }
 }]
 }
};

{
 "presets": [
 [
  "env",
  {
  "targets": {
   "browsers": [ //浏览器版本
   "> 1%",
   "last 2 versions",
   "not ie <= 8",
   "iOS >= 6",
   "safari >= 6",
   "Firefox >= 20",
   "Android > 4",
   "android >= 4.4"
   ]
  }
  }
 ]
 ],
 "plugins": ["transform-runtime"]
}

"scripts": {
  ...
 "build": "webpack" //新增这条命令
 }

npm run build