JSFiddle - React, Tailwind, and code Playground

HTML

<label for="data[User][notify_one_day_out]">One day away:</label>
                            <select name="slider" id="data[User][notify_one_day_out]"
                            data-role="slider">
                                <option value="0">OFF</option>
                                <option value="1" selected="selected">ON</option>
                            </select>

JavaScript

alert( $("#data\\[User\\]\\[notify_one_day_out\\]").val());