document.getElementById('upload_btn').onclick=function(){  
          document.getElementById('save').disabled=false;
           document.getElementById('save').value="save";
               document.getElementById('frm').action="upload.php";
                document.getElementById('frm').target="upload_iframe";  
                document.getElementById('frm').submit();
                  
        }      
以上是submit按钮提交的代码  用来上传图片

upload_btn的type属性不是subimt吗？