JSFiddle - React, Tailwind, and code Playground

by MasterAlex

HTML

<select id="list" multiple="multiple">
    <option value="1">Opt 1</option>
    <option value="2">Opt 2</option>
    <option value="3">Opt 3</option>
    <option value="4">Opt 4</option>
    <option value="5">Opt 5</option>
    <option value="6">Opt 6</option>
</select>
<hr />
Выбрано элементов: <span id="result">0</span>

CSS

select {
    width: 100px;
    height: 90px;
}

JavaScript

$(document).ready(function() {
    $('#list').change(function() {
        var selected = 0;
        $("#list option:selected").each(function(){
            selected++;
        });
        $('#result').text(selected);
    });
});