优化

1.多线程构建

thread-loader、happypack

2.减小体积

js压缩 optimization:true
tree-shaking
loader的test/include/exclude配置，resolve.modules减少模块的搜索层级
压缩图片image-webpack-loader
gzip压缩
cdn引入公共包

3.减少请求

cdn缓存

打包后vender体积过大

vender中主要是公共包
第一种用externals来优化，
第二种用SplitChunks优化。

 splitChunks: {
    cacheGroups: {
      you-module-name: {
        name: you-module-name,
        test: 匹配规则,
        chunks:you-chunks,
        priority: 10, // 优先级
        enforce: true,
      },
     ...
    },
},

参考：https://juejin.cn/post/6844904198023168013#heading-0

pollyfill

https://jkfhto.github.io/2019-10-17/webpack/%E4%BD%BF%E7%94%A8%E5%8A%A8%E6%80%81Polyfill%E6%9C%8D%E5%8A%A1/
Webapck5 核心打包原理全流程解析，看这一篇就够https://mp.weixin.qq.com/s/85S7i3z9pVJyMjVKqXHy6w