JSFiddle - React, Tailwind, and code Playground

HTML

<span id="counter">0</span>

JavaScript

window.onload = function() {
    var counter = document.getElementById('counter'),
        n = counter.innerHTML;
    
    n = parseInt(n);
    
    function counting() {
        n++;
        counter.innerHTML = n;
    }
    
    setInterval(counting, 1000);
}