JSFiddle - React, Tailwind, and code Playground

HTML

<div id="block"></div>

CSS

#block {
    width: 200px;
    height: 200px;
    
    margin: 40px auto;
}

JavaScript

var randomBg = function(target, bgArr) {

    var target = document.querySelector(target),
        index = Math.floor(Math.random() * bgArr.length);
    
    target.style.backgroundImage = 'url(' + bgArr[index] + ')';
    
};

randomBg('#block', [
    'http://subtlepatterns.com/patterns/green_cup.png',
    'http://subtlepatterns.com/patterns/squared_metal.png',
    'http://subtlepatterns.com/patterns/old_map.png',
    'http://subtlepatterns.com/patterns/px_by_Gre3g.png',
    'http://subtlepatterns.com/patterns/diagmonds.png'
]);