select选中事件,通过选中对应值控制另一个div显示隐藏

<select name="cailiao" id="cl" onchange="gradeChange()" class="form-control">
     <option value="2">铝</option>
     <option value="1" >铁</option>     
 </select>
<div class="form-group" id = 'cy' style="display:none;">
           <label for="exampleSelect1">冲压进度</label>
           <select name="chongya"  class="form-control">
           <option value="0" selected>未完成</option>
           <option value="1" >已完成</option>
           </select> 
</div>

js部分

function gradeChange(){
var objS = document.getElementById("cl");
var grade = objS.options[objS.selectedIndex].value;
// console.log(grade);
if(grade==1){

    document.getElementById("cy").style.display="block";
}else{
    document.getElementById("cy").style.display="none";
}
}