function diff(date1, date2) {
        var diff = date2 - date1;
        var diffH = Math.floor((diff % 86400000) / 3600000);            // 시간
        var diffM = Math.floor(((diff % 86400000) % 3600000) / 60000);  // 분
        var diffS = Math.floor(diff / 1000 % 60);                       // 초
    
        if (Math.sign(diff) === -1) { // 음수 check
            return '퇴근시간이 지났어요...'
        } else {
            return '퇴근시간까지: ' + [diffH < 10 ? '0' + diffH : diffH, diffM < 10 ? '0' + diffM : diffM, diffS < 10 ? '0' + diffS : diffS].join(':') + '남음 ;;'
        }
    }
    
    function solution(n) {
        var nowDate = new Date();
        var exitDate = new Date(); // 17:30:00
    
        var input_arr = n.split(':');
    
        exitDate.setHours(input_arr[0]);
        exitDate.setMinutes(input_arr[1]);
        exitDate.setSeconds(input_arr[2]);
    
        console.log(diff(nowDate, exitDate))
    }
    
    solution('17:00:00'); // 퇴근 시간
    Document