JSFiddle - React, Tailwind, and code Playground

HTML

<input type="button" value="Count" onclick="countDown()" />

<div id="displayDiv" ></div>

JavaScript

function countDown() {
    var i = 5;
    var myinterval = setInterval(function() {
        document.getElementById("displayDiv").innerHTML = "Number: " + i;
        if (i === 0) {
            clearInterval(myinterval );
            alert('true') // call your function
        }
        else {
            i--;
        }
    }, 1000);
}