JSFiddle - React, Tailwind, and code Playground

HTML

<select id="sel1">
    <option value="11">1-1</option>
    <option value="12">1-2</option>
    <option value="13">1-3</option>
</select>
<select id="sel2">
    <option value="21">2-1</option>
    <option value="22">2-2</option>
    <option value="23">2-3</option>
</select>

CSS

#sel2 {
    display:none; 
}

JavaScript

$('#sel1').change(function() {
    if ($(this).val() == 12) {
        $('#sel2').show();
    } else {
        $('#sel2').hide();
    }
});