test

<meta charset="utf-8">
<script src="https://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>

<select onchange="func()">
<?php for($i=0;$i<4;$i++){?>
<option value="<?php echo $i?>">选择<?php echo $i;?></option>
<?php }?>
</select>

<script type="text/javascript">
function func(){
//获取被选中的option标签
var vs = $('select option:selected').val();
alert(vs);
}
</script>