JS计算两个日期的时间间隔

/**
 * 计算两个日期字符串target到now的时间间隔
 * @param {*} target 
 * @param {*} now 没有now参数时，计算的是target距离当前的时间间隔
 * @returns 
 */
function calcDiffTime(target, now) {
    //如果时间格式是正确的，那下面这一步转化时间格式就可以不用了
    target = new Date(target.replace(/-/g, "/"));
    if (now) {
        now = new Date(now.replace(/-/g, "/"))
    } else {
        now = new Date();
    }
    //时间差的毫秒数
    let diffTime = now.getTime() - target.getTime();
    //计算出相差天数
    let diffDays = Math.floor(diffTime / (24 * 3600 * 1000));
    //计算天数后剩余的毫秒数
    let remain = diffTime % (24 * 3600 * 1000);
    //计算出相差的小时数 
    let diffHours = Math.floor(remain / (3600 * 1000));
    //计算小时数后剩余的毫秒数
    remain = remain % (3600 * 1000);
    //计算相差分钟数
    let diffMinutes = Math.floor(remain / (60 * 1000));
    //计算分钟数后剩余的毫秒数
    remain = remain % (60 * 1000);
    //计算相差秒数     
    let diffSeconds = Math.round(remain / 1000)
    console.log(" 相差 " + diffDays + "天 " + diffHours + "小时 " + diffMinutes + "分钟 " + diffSeconds + "秒")
    return {
        days: diffDays,
        hours: diffHours,
        minutes: diffMinutes,
        seconds: diffSeconds,
        times: diffTime
    }
}