按需自动引入element-plus组件，以及自己自定义的组件，一切组件不需要手动导入了

//1.需要安装unplugin-vue-components 和 unplugin-auto-import这两款插件，以及element-plus 
npm install -D unplugin-vue-components unplugin-auto-import
npm install element-plus --save

//2.安装完成之后在vue.config.js文件中配置
// vue.config.js
const AutoImport = require('unplugin-auto-import/webpack')
const Components = require('unplugin-vue-components/webpack')
const { ElementPlusResolver } = require('unplugin-vue-components/resolvers')
module.exports = {
  outputDir: './build',
  // 和webpapck属性完全一致，最后会进行合并
  configureWebpack: {
    resolve: {
      alias: {
        components: '@/components'
      }
    },
    //配置webpack自动按需引入element-plus，
      plugins: [
        AutoImport({
          resolvers: [ElementPlusResolver()]
        }),
        Components({
          resolvers: [ElementPlusResolver()]
        })
      ]
  }
}

//3.注意：el-icon还是需要在main.js手动导入
import * as ElIcon from '@element-plus/icons-vue'
Object.keys(ElIcon).forEach(function (key) {
    app.component(ElIcon[key].name, ElIcon[key])
})