js返回时间差

function CalcTimeSub(endTime, startTime, type) {

    var bool = endTime == defaultDateTime || startTime == defaultDateTime;

    var e = new Date(endTime);
    var s = new Date(startTime);

    var stime = Date.parse(s);
    var etime = Date.parse(e);
    var usedTime = etime - stime;  //两个时间戳相差的毫秒数  

    var result = 0;

    switch (type) {
        case 's':
            if (bool) {
                return 0 + '秒';
            } else {
                result = Math.floor(usedTime / 1000) + "秒";
            }
            break;
        case 'm':
            if (bool) {
                return 0 + '分';
            } else {
                result = Math.floor(usedTime / (60 * 1000)) + "分" + Math.floor(usedTime % (60 * 1000) / 1000) + "秒"
            }
            break;
        case 'H':
            if (bool) {
                return 0 + '时';
            } else {
                result = Math.floor(usedTime / (60 * 60 * 1000)) + "时" + Math.floor(usedTime % (60 * 60 * 1000) / (60 * 1000)) + "分";
            }
            break;
        case 'd':
            if (bool) {
                return 0 + '天';
            } else {
                result = Math.floor(usedTime / (24 * 60 * 60 * 1000)) + "天" + Math.floor(usedTime % (24 * 60 * 60 * 1000) / (60 * 60 * 1000)) + "时";
            }
            break;
        case 'M':
            if (bool) {
                return 0 + '月';
            } else {
                result = Math.floor(usedTime / (30 * 24 * 60 * 60 * 1000)) + "月" + Math.floor(usedTime % (30 * 24 * 60 * 60 * 1000) / (24 * 60 * 60 * 1000)) + "天";
            }
            break;
        case 'y':
            if (bool) {
                return 0 + '年';
            } else {
                result = Math.floor(usedTime / (365 * 24 * 60 * 60 * 1000)) + "年" + Math.floor(usedTime % (365 * 30 * 24 * 60 * 60 * 1000) / (30 * 24 * 60 * 60 * 1000)) + "月";
            }
            break;
    }

    return result;
}