JSFiddle - React, Tailwind, and code Playground

HTML

<p id="o"></p>

JavaScript

var start = +new Date, ct = 0, o=document.querySelector('#o');
setInterval(function () {
    var time = (new Date - start) / 1000;
    var avg  = ++ct / time;
    o.innerHTML = ct+" calls in "+time.toFixed(3)+"s is "+avg.toFixed(6)+" calls/second";
}, 1000);