JSFiddle - React, Tailwind, and code Playground

HTML

<p id="test">Test</p>
<button id="foo">Click</button>

JavaScript

var timerId = 0;

function doSomething() {
    var test = document.getElementById("test");
    test.innerText += ' Test';
}

function onmousedown(ev) {
    doSomething();
    timerId = setInterval(function () {
        doSomething();
    }, 1000);
}
function onmouseup(ev) {
    clearInterval(timerId);
}

var obj = document.getElementById("foo");
obj.addEventListener("mousedown", onmousedown);
obj.addEventListener("mouseup", onmouseup);