js 前端验证表单输入

    function checkna()        {            na1 = document.forms['frm'].model.value            if(na1=="")            {                divmodel.innerHTML='<font class="tips_false">型号不能为空</font>';                document.getElementById("model").focus();            }else{                divmodel.innerHTML='<font class="tips_true">√</font>';            }        }

<tr>    <td class="tl"><span class="red">*</span>商品名称</td>    <td>    <input  type="text" name="s_name" onblur="checkna()">    </td></tr>