向下拉列表框中动态添加option不成功！解决办法_跨浏览器开发

向下拉列表框中动态添加option不成功！
<html>
<head>
<script type="text/javascript">
function GenSelectListEx()
{
var curobj=document.getElementById("id_video_format");

for(var i = 0; i < 5; i++)
{
var optionelement = document.createElement("option");
//optionelement.style.cssText ="value:"options[i].optionValue";";
optionelement.text="1111";
curobj.add(optionelement,null);
//var textnode = document.createTextNode(options[i].optionName);
//optionelement.appendChild(textnode);
//curobj.appendChild(optionelement);
//curobj.innerHTML=selectelement.innerHTML;
}

}

</script>
</head>
<body>
<div id="my_div" style="width: 750px; margin-top: 10px; text-align: left; overflow: hidden;">

<select name="video_format" class="td_select" id="id_video_format">

</select>

</div>

<script type="text/javascript">

GenSelectListEx();
</script>

</body>
</html>

为什么我这样做总是提示错误，不知道什么原因！请大家指点。

------解决方案--------------------------------------------------------

HTML code

<html><head><script type="text/javascript">function GenSelectListEx(){  var curobj=document.getElementById("id_video_format");  for(var i = 0; i < 5; i++)  {    var optionelement = new Option("111", "111");    curobj.options.add(optionelement);  }}window.onload=function(){  GenSelectListEx();}</script></head><body>  <div id="my_div" style="width: 750px; margin-top: 10px; text-align: left; overflow: hidden;">      <select name="video_format" class="td_select" id="id_video_format">      </select>  </div></body></html>
------解决方案--------------------------------------------------------
HTML code<html><head>    <script type="text/javascript">        function GenSelectListEx() {            var curobj = document.getElementById("id_video_format");            for (var i = 0; i < 5; i++) {                var optionelement = document.createElement("option");                //optionelement.style.cssText ="value:"options[i].optionValue";";                optionelement.text = "1111";                try {                    curobj.add(optionelement, null);                } catch(e) {                    curobj.add(optionelement);                }            }        }    </script></head><body><div id="my_div" style="width: 750px; margin-top: 10px; text-align: left; overflow: hidden;">    <select name="video_format" class="td_select" id="id_video_format">    </select></div><script type="text/javascript">    GenSelectListEx();</script></body></html>