JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    <button id="start">Start!</button>
    <button id="end">End!</button>
    <div id="targetDiv"></div>
</body>

JavaScript

var myStart = document.querySelector('#start'),
        myEnd = document.querySelector('#end'),
        myRepeat,
        targetDiv = document.querySelector("#targetDiv");

function start() {
    targetDiv.innerHTML += "Hello World<br>";
    myRepeat = setTimeout(start, 1000)
}

function stop() {
    //console.log("STOP");
    clearTimeout(myRepeat);
}

myStart.onclick = start;
myEnd.onclick = stop;