// 安装依赖  npm install  @babel/plugin-proposal-optional-chaining -S
// @babel/plugin-proposal-nullish-coalescing-operator -S
// 在babel.config.js中  的 plugins中添加 "@babel/plugin-proposal-optional-chaining"

module.exports = {
  plugins: [
    '@babel/plugin-proposal-optional-chaining',  //可选链 ?.
    '@babel/plugin-proposal-nullish-coalescing-operator'  //空值合并 ??
  ]
}

// template中使用
// 插件开发
export default {
  install (Vue) {
    const optionalChaining = (obj, ...rest) => {
      let temp = obj
      for(const key in rest) {
        temp = temp?.[rest[key]]
      }
      return temp
    }
    vue.prototype.$chaining= optionalChaining
  }
}


// main.js
import Vue from 'vue'
import Chaining from 'chaining'

Vue.use(Chaining)

// *.vue
<template>
  <div>{{$$(obj, 'first', 'second') }}</div>
</template>