A stopwatch in Javascript

stopwatch.js

// Set starting variables for stopwatch
let minutes = 0
let seconds = 0
let secondsAsString = '00'
let minutesAsString = '00'

// Starts the stopwatch
let startTimer = () => setInterval(timerLogic, 1000)

// Logic behind the stopwatch
let timerLogic = () => {
    if (seconds === 59) { minutes++; seconds = 0 } else { seconds++ }
    seconds < 10 ? secondsAsString = '0' + seconds.toString() : secondsAsString = seconds.toString()
    minutes < 10 ? minutesAsString = '0' + minutes.toString() : minutesAsString = minutes.toString()
    timerCounter.textContent = minutesAsString + ":" + secondsAsString
}