JSFiddle - React, Tailwind, and code Playground

HTML

<input type="submit" id="plus1" value="+" style="font-weight:bold; width:50px; height:50px;" tabindex="-1">
<div id="testarea">testarea:</div>

JavaScript

var i = 1;
$("#plus1").mousedown(function () {
    loopthis = setInterval(repeatingfunction, 100);
}).mouseup(function () {
    clearInterval(loopthis);
});

function repeatingfunction() {
    $("#testarea").append(i);
    i = i + 1;
}