下拉列表设置

HMTL代码

<select id="category" name="category">
    <option value="">请选择类别</option>
    <option value="1">类别1</option>
    <option value="2">类别2</option>
    <option value="3">类别3</option>
    <option value="4">类别4</option>
</select>

JS代码

<script src="static/js/jquery-3.1.1.min.js"></script>
<script type="text/javascript">
    $('#category option[value=3]').attr('selected',true);
</script>