main.js

const display = document.getElementById('display');
let isRunning = false;
let startTime = 0;
let elapsedTime = 0;
let timer = null;


function startStopwatch()
{
    if(isRunning)
        {
            return;
        }
    startTime = Date.now() - elapsedTime;
    timer = setInterval(update,1);
    isRunning = true;
}

function stopStopwatch()
{
if(isRunning)
    {
        clearInterval(timer);
        isRunning = false;
    }
}

function resetStopwatch(){
clearInterval(timer);
isRunning = false;
startTime = 0;
elapsedTime = 0;
timer = null;
display.textContent = "00:00:00:00";
}

function update()
{
    const currentTime  = Date.now();
    elapsedTime = currentTime - startTime;
    
    let hours = Math.floor(elapsedTime / (1000*60*60));
    let minutes = Math.floor(elapsedTime / (1000*60) % 60);
    let seconds = Math.floor(elapsedTime / (1000) %60);
    let milliseconds = Math.floor(elapsedTime % 1000 / 10);

    hours = String(hours).padStart(2,"0");
    minutes = String(minutes).padStart(2,"0");
    seconds = String(seconds).padStart(2,"0");
    milliseconds = String(milliseconds).padStart(2,"0");

    display.textContent = hours + ":" + minutes + ":" +seconds + ":" + milliseconds;
}