JSFiddle - React, Tailwind, and code Playground

HTML

<div id="obj"></div>

CSS

#obj {
    height: 200px;
    width: 200px;
}

JavaScript

HTMLElement.prototype.ver = function() {
    this.style.backgroundColor = "#333333";
}

window.onload = function () {
    window.onclick = function () {
        obj = document.getElementById("obj");
        obj.ver();
    }
}