function fold(node){      var map = new Map();      map.set(node.tagName,1);      [].reduce.call(node.children,(acc,child)=>{        deal(acc,fold(child));        return acc      },map)      return map    }    function deal(srcMap,tarMap){      tarMap.forEach((value,tagName)=>{        var newV = value + ~~srcMap.get(tagName);        srcMap.set(tagName,newV);      })    }