js统计页面上每个标签的数量实例代码

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);
 })
 }