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'