vue2 按照demo写的话报错 about minimce HOT 2 CLOSED

// vue.config.js

module.exports = {
  // ...
  chainWebpack: config => {
    // ...
    config.resolve
      .extensions
        .prepend('.mjs')

    config.module
      .rule('mjs')
        .test(/\.mjs$/)
        .include
          .add(/node_modules/)
          .end()
        .type('javascript/auto')
      // ...
  },
  // ...
}