JavaScript实现统计页面DOM标签数量的方法

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);
      })
    }