获取label标签内for的属性值-js

<body>
    <div class="row_2" id="ass">
        <label for="aaa">1</label>
        <label for="aaa">2</label>
        <label for="aaa">3</label>
        <label for="bbb">4</label>
        <label for="bbb">5</label>
        <label for="bbb">6</label>
    </div>        
</body>
<script type="text/javascript">
    var ass=document.getElementById("ass");
    var laArr = ass.getElementsByTagName("label");
            for(i=0;i<laArr.length;i++){
              //取出参数for的值
                 var forvalue=laArr[i].getAttributeNode("for").value;
                 var forNext1 = laArr[i+1].getAttributeNode("for").value;
                 if(forvalue==forNext1)
                 {                      
                    ass.removeChild(laArr[i+2]); 
                    ass.removeChild(laArr[i+1]);                         
                 } 
                 console.log(forvalue);//aaa
                 console.log(forNext1);//bbb
          }
           
</script>