JSFiddle - React, Tailwind, and code Playground

by swiffe

HTML

<select id="count_pullover" name="count_pullover">
    <option value="0" selected="selected">0x Pullover</option>
    <option value="1">1x Pullover</option>
    <option value="2">2x Pullover</option>
    <option value="3">3x Pullover</option>
    <option value="4">4x Pullover</option>
    <option value="5">5x Pullover</option>
</select>
<select id="size_pullover" name="size_pullover" disabled>
    <option value="XS">XS</option>
    <option value="S">S</option>
    <option value="M">M</option>
    <option value="L">L</option>
    <option value="XL">XL</option>
    <option value="XXL">XXL</option>
</select>

JavaScript

document.getElementById('count_pullover').onchange = function () {
    document.getElementById('size_pullover').disabled = this.value == '0';
}