JSFiddle - React, Tailwind, and code Playground

HTML

<button id="fast">Fast</button>
<button id="normal">Normal</button>
<button id="slow">Slow</button>
<div id="fadey1" class="fadey"></div>
<div id="fadey2" class="fadey"></div>

CSS

.fadey {
    position: absolute;
    height: 50px;
    width: 50px;
}
#fadey1 {
    background: blue;
}
#fadey2 {
    background: red;
}

JavaScript

$(document).ready(function () {
    var faderIndex = 0,
        faderOutSpeed = 2000,
        faderInSpeed = 3000,
        faders = $('.fadey');

    $('button#fast').click(function () {
        faderOutSpeed = 200;
        faderInSpeed = 300;
    });

    $('button#normal').click(function () {
        faderOutSpeed = 600;
        faderInSpeed = 900;
    });

    $('button#slow').click(function () {
        faderOutSpeed = 2000;
        faderInSpeed = 3000;
    });

    function nextFade() {
        $(faders[faderIndex]).fadeOut(faderInSpeed, function () {
            faderIndex++;
            if (faderIndex >= faders.length) faderIndex = 0;
            $(faders[faderIndex]).fadeIn(faderOutSpeed, nextFade);
        });
    }
    nextFade();
});