JSFiddle - React, Tailwind, and code Playground

HTML

<div id="ejemplo">LOL</div>
<div id="otro">WUT</div>

JavaScript

var x = document.getElementById("ejemplo");
x.__proto__.alert = function(){
    alert(this.id);
};
x.alert();

function alertar(){
    alert(this.id);
}

var y = document.getElementById("otro");
alertar.call(y);