Select下拉框onchange事件获取option的value值

<select name="type" onchange="show_sub(this.options[this.options.selectedIndex].value)">
<option value="0">请选择主类别</option>
<option value="1">1</option>
<option value="2">2</option>
</select>

<script>
function show_sub(val){
alert(val);
}
</script>