let seconds = 0

let tens = 0

const displayTens = document.getElementById('tens')

const displaySeconds = document.getElementById('seconds')

const buttonStart = document.getElementById('button-start')

const buttonStop = document.getElementById('button-stop')

const buttonReset = document.getElementById('button-reset')

let interval

buttonStart.onclick = () => {

clearInterval(interval)

interval = setInterval(timer, 10)

}

buttonStop.onclick = () => {

clearInterval(interval)

}

buttonReset.onclick = () => {

clearInterval(interval)

tens = 0

seconds = 0

displayTens.innerHTML = `0${tens}`

displaySeconds.innerHTML = `0${seconds}`

}

const timer = () => {

tens++

if (Number(tens) <= 9) {

displayTens.innerHTML = `0${tens}`

}

if (Number(tens) > 9) {

displayTens.innerHTML = tens

}

if (Number(tens) > 99) {

console.log('seconds')

seconds++

displaySeconds.innerHTML = `0${seconds}`

tens = 0

displayTens.innerHTML = `0${tens}`

}

if (Number(seconds) > 9) {

displaySeconds.innerHTML = seconds

}

}