let callbacks = [];//放一個數(shù)組放置回調函數(shù)

function loadedTinymce() {//檢測腳本是否加載好的方法 如果tinymce加載好了，window對象上會有tinymce屬性 若要加載其它腳本只需要將此判斷改一下即可
 // to fixed https://github.com/PanJiaChen/vue-element-admin/issues/2144
 // check is successfully downloaded script
 return window.tinymce
}

const dynamicLoadScript = (src, callback) => {
 const existingScript = document.getElementById(src);//獲取script標簽元素
 const cb = callback || function() {};//拿到回調函數(shù)

 if (!existingScript) {//若沒有這個腳本的script標簽
  const script = document.createElement('script');//創(chuàng)建一個script標簽
  script.src = src // src url for the third-party library being loaded.
  script.id = src
  document.body.appendChild(script)
  callbacks.push(cb);//將回調函數(shù)加到callbacks數(shù)組中
  const onEnd = 'onload' in script ? stdOnEnd : ieOnEnd;//若是標準瀏覽器 有onload屬性 若是ie瀏覽器 沒有onload屬性
  onEnd(script)
 }

 if (existingScript && cb) {//若此script標簽存在 并且有回調函數(shù)
  if (loadedTinymce()) {//檢測是否有tinymce屬性
   cb(null, existingScript);//若有tinymce對象，則執(zhí)行回調函數(shù)
  } else {
   callbacks.push(cb);//若沒有tinymce對象，則將回調函數(shù)加到回調函數(shù)數(shù)組內
  }
 }

 function stdOnEnd(script) {//標準瀏覽器加載好腳本后
  script.onload = function() {//腳本加載成功后
   // this.onload = null here is necessary
   // because even IE9 works not like others
   this.onerror = this.onload = null;//將script標簽的onload和onerror屬性置空
   for (const cb of callbacks) {//執(zhí)行回調函數(shù) 之所以用數(shù)組放置回調函數(shù)是應對 我仍然事件的發(fā)生
    cb(null, script)
   }
   callbacks = null;//將callbacks置空
  }
  script.onerror = function() {//腳本加載失敗后
   this.onerror = this.onload = null;//將script標簽的onload和onerror置空 覆蓋原生的onload事件和nerror事件
   cb(new Error('Failed to load ' + src), script);//腳本加載錯誤后執(zhí)行回調函數(shù)，返回報錯信息
  }
 }

 function ieOnEnd(script) {//若是ie瀏覽器 
  script.onreadystatechange = function() {//腳本加載成功后
   if (this.readyState !== 'complete' && this.readyState !== 'loaded') return;//腳本沒加載好則不執(zhí)行回調函數(shù) ie瀏覽器會自動報錯
   this.onreadystatechange = null;//若 加載成功
   for (const cb of callbacks) {//執(zhí)行回調函數(shù)
    cb(null, script) // there is no way to catch loading errors in IE8
   }
   callbacks = null;//置空callbacks
  }
 }
}

export default dynamicLoadScript;//暴露出動態(tài)加載腳本的方法

import load from './dynamicLoadScript'

load(tinymceCDN, (err) => {//tinymceCDN代表tinymce的CDN地址，下一個參數(shù)是回調方法
    if (err) {//若腳本加載錯誤，這彈出錯誤提示
     this.$message.error(err.message)
     return
    }
    this.initTinymce();//否則執(zhí)行初始化tinymce方法
   })