JSFiddle - React, Tailwind, and code Playground

by Brunno Romero

HTML

<select id="mySelect">
    <option value="Audi">Audi
        <option value="BMW">BMW
            <option value="Mercedes">Mercedes
                <option value="Volvo">Volvo</select>
<br>
<br>
<div id="modelo" style="display:none;">Escolha um modelo
    <br>
    <select>
        <option value="x1">x1</option>
        <option value="x2">x2</option>
        <option value="x3">x3</option>
        <option value="x4">x4</option>
    </select>
</div>

JavaScript

var select = document.getElementById('mySelect');

select.addEventListener('change', myFunction);

function myFunction() {
    
    var x = document.getElementById("mySelect");
        
    if (x.value == ("BMW")) {
        document.getElementById("modelo").style.display = '';
    }    
}