JSFiddle - React, Tailwind, and code Playground

HTML

<button id="test">run</button>

JavaScript

function A() { }
A.prototype.foo = 1;
A.prototype.bar = { lol: 2 };

document.getElementById('test').onclick = function() {
    var epic = new A();
    var fail = new A();
    
    epic.foo = 5;
    epic.bar.lol = 6;
    
    alert('foo: ' + fail.foo + '\nbar: ' + fail.bar.lol);
};