js onchange事件，以及setAttribute，getAttribute

     onchange为form表单中select标签发生改变时产生的事件，从

                           <select style="width:160px" class="select2" name="mix_{$val.sign}" onchange="gradeChange(this)" >
                            <option value="0" {$i==$val[num]?'selected':''} lrc="{$val.num}" >请选择</option>
                            <for start="1" end="$val[num]+1" >
                            <option value="{$i}" {$i==$val[num]?'selected':''} lrc="{$val.num}" > {$i}</option>
                            </for>
                            </select>

                          <span id="{$val.sign}" data="{$val.num}" mix="0" common="0">{$val.num} </span>

   选择数目的改变会影响到相对应的span也发生对应的值的变化，比较容易出错的地方为parseInt数据类型转换和span添加和改变属性值来存储自己需要的东西 。

<script type="text/javascript" language="javascript">
    function gradeChange(obj) {
    
     
        var grade = obj.options[obj.selectedIndex].value;
        var num=obj.options[obj.selectedIndex].getAttribute("lrc");
       
        var name=obj.name;
        array = name.split("_");
      
      
        var amount = document.getElementById(array[1]);
        var result=parseInt(num)-parseInt(grade);
       
        amount.setAttribute("mix",result);
        var mix=parseInt(amount.getAttribute("mix"));
         
        var common=parseInt(amount.getAttribute("common"));
    

        
            
        var x=parseInt(amount.getAttribute("data"));
       
        amount.innerHTML=x+common+mix;

   
    

      
        // var url = "__ROOT__/Admin/Index/admin/num/" + grade;

        // window.location.href = url;
    }
 </script>