function _pad(num, n = 2) {
let len = num.toString().length
while (len < n) {
num = '0' + num
len++
}
return num
}
let seconds = 8
_pad(seconds) // '08'

function format(interval) {
interval = interval | 0
let minitues = interval / 60 | 0
let seconds = interval % 60
return `${minitues}:${(seconds + '').padStart(2, '0')}`
}
format(123) // '2:03'