js統計頁面上每個標簽的數量

        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);
            })
        }         

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