dedecms自定义表单怎么添加发布时间功能

<input type="text" name="shijian" id="shijian" value="">  <script type="text/javascript">  window.onload = function(){  var nowDate = new Date();  var str = nowDate.getFullYear()+"-"+(nowDate.getMonth() + 1)+"-"+nowDate.getDate()+" "+nowDate.getHours()+":"+nowDate.getMinutes()+":"+nowDate.getSeconds();  document.getElementByIdx_x("shijian").value=str;  } //phpfensi.com  </script>