JS计算两日期之前的天数,小时数,分钟数,秒数

calculateDate(startTime, endTime, diffType) {
    startTime = startTime.replace(/\-/g, "/");
    endTime = endTime.replace(/\-/g, "/");
    diffType = diffType.toLowerCase();
    var sTime = new Date(startTime);
    var eTime = new Date(endTime);
    if (sTime > eTime) {
    alert("开始时间不能大于结束时间!!!");
    return false;
    }
    //作为除数的数字
    var divNum = 1;
    switch (diffType) {
    case "second":
        divNum = 1000;
        break;
    case "minute":
        divNum = 1000 * 60;
        break;
    case "hour":
        divNum = 1000 * 3600;
        break;
    case "day":
        divNum = 1000 * 3600 * 24;
        break;
    default:
        break;
    }
    return  parseInt((eTime.getTime() - sTime.getTime()) / parseInt(divNum));
}