JSFiddle - React, Tailwind, and code Playground

HTML

<select id="multiSelect" size="5" multiple="multiple">
    <option value="o1">Option 1</option>
    <option value="o2">Option 2</option>
    <option value="o3">Option 3</option>
    <option value="o4">Option 4</option>
    <option value="o5">Option 5</option>
    <option value="o6">Option 6</option>
</select>
<br />
<button id="btnGetValues">Get Values</button>
<br />
<br />
<br />
<input class="text" id="quantite" type="text" name="quantité" value="o7" />

JavaScript

$('#btnGetValues').click(function() {
    $('#multiSelect').append('<option value="' + $('#quantite').val() + '">New option</option>');
});