通过js让标签动态设置默认值

<select id="selectY" name="job" onchange="javascript:location.href=this.value;">								
	<option value="searchUserinfo.action?job_value=0">所有用户</option>
	<option value="searchUserinfo.action?job_value=10010">java工程师</option>
	<option value="searchUserinfo.action?job_value=10011" >c开发工程师</option>
	<option value="searchUserinfo.action?job_value=10012" >web前端工程师</option>
</select>
<input id="option_num" type="hidden" value="<s:property value="#session.option_num"/>">
<script>
     var i=document.getElementById("option_num").value;
     var select=document.getElementById("selectY");
     var arr=select.getElementsByTagName("option");	
     arr[i].selected="selected";
</script><select id="selectY" name="job" onchange="javas