小编Gau*_*mar的帖子

(function($) {
    $(function() {
        $('.my-select-box').fSelect();
        $('#ClearSelect').click(function(){
           $("#fselectMulti option:selected").removeAttr("selected");
        })
    });
    
})(jQuery);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link href="https://facetwp.com/wp-content/plugins/facetwp/assets/vendor/fSelect/fSelect.css" rel="stylesheet"/>
<script src="https://facetwp.com/wp-content/plugins/facetwp/assets/vendor/fSelect/fSelect.js"></script>
<select id="fselectMulti" class="my-select-box" multiple="multiple">
    <optgroup label="Northeast">
        <option selected value="me">Maine</option>
        <option selected value="ny">New York</option>
        <option value="nj">New Jersey</option>
        <option value="vt">Vermont</option>
    </optgroup>
    <optgroup label="Southwest">
        <option value="az">Arizona</option>
        <option selected value="nm">New Mexico</option>
        <option value="ca">California</option>
        <option value="nv">Nevada</option>
    </optgroup>
</select>

<button id="ClearSelect">Clear</button>