（摘）前端整理（二）：Date

/**
 * 格式化时间
 * 
 * @param  {time} 时间
 * @param  {cFormat} 格式
 * @return {String} 字符串
 *
 * @example formatTime('2018-1-29', '{y}/{m}/{d} {h}:{i}:{s}') // -> 2018/01/29 00:00:00
 */
formatTime(time, cFormat) {
    if (arguments.length === 0) return null
    if ((time + '').length === 10) {
        time = +time * 1000
    }

    var format = cFormat || '{y}-{m}-{d} {h}:{i}:{s}', date
    if (typeof time === 'object') {
        date = time
    } else {
        date = new Date(time)
    }

    var formatObj = {
        y: date.getFullYear(),
        m: date.getMonth() + 1,
        d: date.getDate(),
        h: date.getHours(),
        i: date.getMinutes(),
        s: date.getSeconds(),
        a: date.getDay()
    }
    var time_str = format.replace(/{(y|m|d|h|i|s|a)+}/g, (result, key) => {
        var value = formatObj[key]
        if (key === 'a') return ['一', '二', '三', '四', '五', '六', '日'][value - 1]
        if (result.length > 0 && value < 10) {
            value = '0' + value
        }
        return value || 0
    })
    return time_str
}


/**
 * 返回指定长度的月份集合
 * 
 * @param  {time} 时间
 * @param  {len} 长度
 * @param  {direction} 方向：  1: 前几个月;  2: 后几个月;  3:前后几个月  默认 3
 * @return {Array} 数组
 * 
 * @example   getMonths('2018-1-29', 6, 1)  // ->  ["2018-1", "2017-12", "2017-11", "2017-10", "2017-9", "2017-8", "2017-7"]
 */
getMonths(time, len, direction) {
    var mm = new Date(time).getMonth(),
        yy = new Date(time).getFullYear(),
        direction = isNaN(direction) ? 3 : direction,
        index = mm;
    var cutMonth = function(index) {
        if ( index <= len && index >= -len) {
            return direction === 1 ? formatPre(index).concat(cutMonth(++index)):
                direction === 2 ? formatNext(index).concat(cutMonth(++index)):formatCurr(index).concat(cutMonth(++index))
        }
        return []
    }
    var formatNext = function(i) {
        var y = Math.floor(i/12),
            m = i%12
        return [yy+y + '-' + (m+1)]
    }
    var formatPre = function(i) {
        var y = Math.ceil(i/12),
            m = i%12
        m = m===0 ? 12 : m
        return [yy-y + '-' + (13 - m)]
    }
    var formatCurr = function(i) {
        var y = Math.floor(i/12),
            yNext = Math.ceil(i/12),
            m = i%12,
            mNext = m===0 ? 12 : m
        return [yy-yNext + '-' + (13 - mNext),yy+y + '-' + (m+1)]
    }
    // 数组去重
    var unique = function(arr) {
        if ( Array.hasOwnProperty('from') ) {
            return Array.from(new Set(arr));
        }else{
            var n = {},r=[]; 
            for(var i = 0; i < arr.length; i++){
                if (!n[arr[i]]){
                    n[arr[i]] = true; 
                    r.push(arr[i]);
                }
            }
            return r;
        }
    }
    return direction !== 3 ? cutMonth(index) : unique(cutMonth(index).sort(function(t1, t2){
        return new Date(t1).getTime() - new Date(t2).getTime()
    }))
}



/**
 * 返回指定长度的天数集合
 * 
 * @param  {time} 时间
 * @param  {len} 长度
 * @param  {direction} 方向： 1: 前几天;  2: 后几天;  3:前后几天  默认 3
 * @return {Array} 数组
 *
 * @example date.getDays('2018-1-29', 6) // -> ["2018-1-26", "2018-1-27", "2018-1-28", "2018-1-29", "2018-1-30", "2018-1-31", "2018-2-1"]
 */
getDays(time, len, diretion) {
    var tt = new Date(time)
    var getDay = function(day) {
        var t = new Date(time)
        t.setDate(t.getDate() + day)
        var m = t.getMonth()+1
        return t.getFullYear()+'-'+m+'-'+t.getDate()
    }
    var arr = []
    if (diretion === 1) {
        for (var i = 1; i <= len; i++) {
            arr.unshift(getDay(-i))
        }
    }else if(diretion === 2) {
        for (var i = 1; i <= len; i++) {
            arr.push(getDay(i))
        }
    }else {
        for (var i = 1; i <= len; i++) {
            arr.unshift(getDay(-i))
        }
        arr.push(tt.getFullYear()+'-'+(tt.getMonth()+1)+'-'+tt.getDate())
        for (var i = 1; i <= len; i++) {
            arr.push(getDay(i))
        }
    }
    return diretion === 1 ? arr.concat([tt.getFullYear()+'-'+(tt.getMonth()+1)+'-'+tt.getDate()]) : 
        diretion === 2 ? [tt.getFullYear()+'-'+(tt.getMonth()+1)+'-'+tt.getDate()].concat(arr) : arr
}


/**
 * @param  {s} 秒数
 * @return {String} 字符串 
 *
 * @example formatHMS(3610) // -> 1h0m10s
 */
formatHMS (s) {
    var str = ''
    if (s > 3600) {
        str = Math.floor(s/3600)+'h'+Math.floor(s%3600/60)+'m'+s%60+'s'
    }else if(s > 60) {
        str = Math.floor(s/60)+'m'+s%60+'s'
    }else{
        str = s%60+'s'
    }
    return str
}

/*获取某月有多少天*/
getMonthOfDay (time) {
    var date = new Date(time)
    var year = date.getFullYear()
    var mouth = date.getMonth() + 1
    var days

    //当月份为二月时，根据闰年还是非闰年判断天数
    if (mouth == 2) {
        days = year % 4 == 0 ? 29 : 28
    } else if (mouth == 1 || mouth == 3 || mouth == 5 || mouth == 7 || mouth == 8 || mouth == 10 || mouth == 12) {
        //月份为：1,3,5,7,8,10,12 时，为大月.则天数为31；
        days = 31
    } else {
        //其他月份，天数为：30.
        days = 30
    }
    return days
}

/*获取某年有多少天*/
getYearOfDay (time) {
    var firstDayYear = this.getFirstDayOfYear(time);
    var lastDayYear = this.getLastDayOfYear(time);
    var numSecond = (new Date(lastDayYear).getTime() - new Date(firstDayYear).getTime())/1000;
    return Math.ceil(numSecond/(24*3600));
}

/*获取某年的第一天*/
getFirstDayOfYear (time) {
    var year = new Date(time).getFullYear();
    return year + "-01-01 00:00:00";
}

/*获取某年最后一天*/
getLastDayOfYear (time) {
    var year = new Date(time).getFullYear();
    var dateString = year + "-12-01 00:00:00";
    var endDay = this.getMonthOfDay(dateString);
    return year + "-12-" + endDay + " 23:59:59";
}

/*获取某个日期是当年中的第几天*/
getDayOfYear (time) {
    var firstDayYear = this.getFirstDayOfYear(time);
    var numSecond = (new Date(time).getTime() - new Date(firstDayYear).getTime())/1000;
    return Math.ceil(numSecond/(24*3600));
}

/*获取某个日期在这一年的第几周*/
getDayOfYearWeek (time) {
    var numdays = this.getDayOfYear(time);
    return Math.ceil(numdays / 7);
}

原文地址：https://segmentfault.com/a/1190000013041329
作者：咚子