来源：https://www.educative.io/edpresso/how-to-dynamically-load-a-js-file-in-javascript

动态加载JS脚本（Promise）.js

function loadScript (FILE_URL, async = true, type = 'text/javascript') {
  return new Promise((resolve, reject) => {
    try {
      const scriptEle = document.createElement('script')
      scriptEle.type = type
      scriptEle.async = async
      scriptEle.src = FILE_URL

      scriptEle.addEventListener('load', (ev) => {
        resolve()
      })

      scriptEle.addEventListener('error', (ev) => {
        reject(new Error(`Failed to load the script ${FILE_URL}`))
      })

      document.body.appendChild(scriptEle)
    } catch (error) {
      reject(error)
    }
  })
}


// 例子：动态加载moment库
;(async () => {
    await loadScript('https://unpkg.com/moment@2.29.1/min/moment.min.js')
})()