element,下拉位置錯(cuò)位并在vue-popper報(bào)：PopperJS is not a constructor"

elementUI使用select時(shí)，下拉位置錯(cuò)位并在vue-popper報(bào)TypeError: PopperJS is not a constructor"

[Vue warn]: Error in event handler for "updatePopper": "TypeError: PopperJS is not a constructor"

found in

---> <ElSelectDropdown> at src/lib/ele-components/select/src/select-dropdown.vue
       <ElSelect> at src/lib/ele-components/select/src/select.vue
         <App> at example/App.vue
           <Root>

源碼 src/utils/vue-popper

updatePopper時(shí)是undefined
createPopper里報(bào)了TypeError: PopperJS is not a constructor"

不知道哪里出了問題，
``
createPopper() {

  //...
  //  這里創(chuàng)建實(shí)例時(shí)報(bào)錯(cuò) 不是一個(gè)構(gòu)造函數(shù)
  this.popperJS = new PopperJS(reference, popper, options);
  this.popperJS.onCreate(_ => {
    this.$emit('created', this);
    this.resetTransformOrigin();
    this.$nextTick(this.updatePopper);
  });
  if (typeof options.onUpdate === 'function') {
    this.popperJS.onUpdate(options.onUpdate);
  }
  this.popperJS._popper.style.zIndex = PopupManager.nextZIndex();
  this.popperElm.addEventListener('click', stop);
},

updatePopper () {

  const popperJS = this.popperJS; // 這里是undefined!
  if (popperJS) {
    popperJS.update();
    if (popperJS._popper) {
      popperJS._popper.style.zIndex = PopupManager.nextZIndex();
    }
  } else {
    this.createPopper();
  }
},