JS获取当前时间的前几天、前几周、前几个月、前几年的时间

alert(getDate());            //当前时间
alert(getDate("day", -2));   //前两天的时间
alert(getDate("day", 2));    //后两天的时间
alert(getDate("month", -2)); //前两个月的时间
alert(getDate("month", 2));  //后两个月的时间

function getDate(type = null, number = 0) {
    var nowdate = new Date();
    const hours = ('0' + nowdate.getHours()).slice(-2);
    const minutes = ('0' + nowdate.getMinutes()).slice(-2);
    const seconds = ('0' + nowdate.getSeconds()).slice(-2);
    switch (type) {
        case "day":   //取number天前、后的时间
            nowdate.setTime(nowdate.getTime() + (24 * 3600 * 1000) * number);
            var y = nowdate.getFullYear();
            var m = ('0' + (nowdate.getMonth() + 1)).slice(-2);
            var d = ('0' + nowdate.getDate()).slice(-2);

            var retrundate = y + '-' + m + '-' + d+" "+hours+":"+minutes+":"+seconds;
            break;
        case "week":  //取number周前、后的时间
            var weekdate = new Date(nowdate + (7 * 24 * 3600 * 1000) * number);
            var y = weekdate.getFullYear();
            var m = ('0' + (nowdate.getMonth() + 1)).slice(-2);
            var d = ('0' + nowdate.getDate()).slice(-2);
            var retrundate = y + '-' + m + '-' + d+" "+hours+":"+minutes+":"+seconds;
            break;
        case "month":  //取number月前、后的时间
            nowdate.setMonth(nowdate.getMonth() + number);
            var y = nowdate.getFullYear();
            var m = ('0' + (nowdate.getMonth() + 1)).slice(-2);
            var d = ('0' + nowdate.getDate()).slice(-2);
            var retrundate = y + '-' + m + '-' + d+" "+hours+":"+minutes+":"+seconds;
            break;
        case "year":  //取number年前、后的时间
            nowdate.setFullYear(nowdate.getFullYear() + number);
            var y = nowdate.getFullYear();
            var m = ('0' + (nowdate.getMonth() + 1)).slice(-2);
            var d = ('0' + nowdate.getDate()).slice(-2);
            var retrundate = y + '-' + m + '-' + d+" "+hours+":"+minutes+":"+seconds;
            break;
        default:     //取当前时间
            var y = nowdate.getFullYear();
            var m = ('0' + (nowdate.getMonth() + 1)).slice(-2);
            var d = ('0' + nowdate.getDate()).slice(-2);
            var retrundate = y + '-' + m + '-' + d+" "+hours+":"+minutes+":"+seconds;
    }
    return retrundate;
}

function getCurtime() {
    const now = new Date();
    const year = now.getFullYear();
    const month = ('0' + (now.getMonth() + 1)).slice(-2);
    const day = ('0' + now.getDate()).slice(-2);
    const hours = ('0' + now.getHours()).slice(-2);
    const minutes = ('0' + now.getMinutes()).slice(-2);
    const seconds = ('0' + now.getSeconds()).slice(-2);
    const formattedTime = year + "-" + month + "-" + day + " " + hours + ":" + minutes + ":" + seconds;
    return formattedTime;
}