JSFiddle - React, Tailwind, and code Playground

by wZVanG

HTML

<span id="timer">0</span>

JavaScript

var obj = document.getElementById("timer"), dec = 1, est = 1

function loop(){
    obj.innerHTML = dec == 10 ? "1" : "0" + (dec == 0 ? "" : "." + dec)
    if(dec == 10) est = 0
    if(dec === 0) est = 1
    est ? dec++ : dec--
}

setInterval(loop,500)