JSFiddle - React, Tailwind, and code Playground

by LW

HTML

<form>
  <input type="checkbox" id="pizza" name="pizza" value="yes">
  <label for="pizza">I would like to order a</label>
  <select id="pizza_kind">
    <option>(choose one)</option>
    <option value="margaritha">Margaritha</option>
    <option value="hawai">Hawai</option>
  </select>
  pizza.
</form>

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>

JavaScript

var update_pizza = function () {
    if ($("#pizza").is(":checked")) {
        $('#pizza_kind').prop('disabled', false);
    }
    else {
        $('#pizza_kind').prop('disabled', 'disabled');
    }
};

$(update_pizza);
$("#pizza").change(update_pizza);