JSFiddle - React, Tailwind, and code Playground

HTML

<div class="testimonials">
<div class="item">item 1</div>
<div class="item">item 2</div>
<div class="item">item 3</div>
<div class="item">item 4</div>
</div>

CSS

.item {display:none;}

JavaScript

var $items = $('.testimonials .item');

function getRandomItem(){
    return $items.eq(Math.floor($items.length * Math.random()));
}

getRandomItem().show();

setInterval(function(){ 
    var $outgoing = $items.filter(':visible');
    var $incoming = getRandomItem();
    $outgoing.fadeOut(1000, function(){
        $incoming.fadeIn(1000);
    });
}, 3000);