text: import Vue from './instance/index'
  import { initGlobalAPI } from './global-api/index'
  import { isServerRendering } from 'core/util/env'
  import { FunctionalRenderContext } from 'core/vdom/create-functional-component'
  
  initGlobalAPI(Vue)
  // $isServer 是否为服务器渲染 相关知识链接 https://blog.csdn.net/weixin_30627341/article/details/96016588?utm_medium=distribute.pc_relevant.none-task-blog-searchFromBaidu-3.control&depth_1-utm_source=distribute.pc_relevant.none-task-blog-searchFromBaidu-3.control
  // 为什么要用Object.defineProperty? 而不是Vue.prototype.$isServer?
  Object.defineProperty(Vue.prototype, '$isServer', {
    get: isServerRendering
  })
  // $ssrContext 服务器渲染的上下文
  // 代码覆盖率工具 Istanbul => istanbul ignore next 可以不计入覆盖率计算
  Object.defineProperty(Vue.prototype, '$ssrContext', {
    get () {
      /* istanbul ignore next */
      return this.$vnode && this.$vnode.ssrContext
    }
  })
  
  // expose FunctionalRenderContext for ssr runtime helper installation
  Object.defineProperty(Vue, 'FunctionalRenderContext', {
    value: FunctionalRenderContext
  })
  
  Vue.version = '__VERSION__'
  
  export default Vue
  