/**
 * Get outerHTML of elements, taking care
 * of SVG elements in IE as well.
 */
function getOuterHTML (el: Element): string {
  if (el.outerHTML) {
    return el.outerHTML
  } else {
    const container = document.createElement('div')
　　 //true 递归复制当前节点的所有子孙节点, false 复制当前节点
    container.appendChild(el.cloneNode(true))
　　//innerHTML 返回元素内容
    return container.innerHTML
  }
}