SOURCE

// let time = new Date('2019-12-12 21:00').getHours()
// let time = new Date('2019-12-12 21:00').getMinutes()

let hour = new Date('21:00')
let time = new Date('2019-12-12 21:00').getTime()/1000
let time2 = new Date('2019-12-12 21:00').valueOf()/1000
let time3 = Date.parse(new Date('2019-12-12 21:00'))/1000
// console.log(hour)
// console.log(time,time2,time3)


function someDaySomeTime(n, time) {
       // 将传入时间字符串转为数组
        var timeArr = time.split('/')
        // 获取当前时间戳
        var today = new Date();
        // 将当天时间戳设为0点0分0秒
        today.setHours(0),
        today.setMinutes(0);
        today.setSeconds(0);
        today.setMilliseconds(0);
        console.log(today)
        // 计算一天的毫秒数
        var oneDay = 1000 * 60 * 60 * 24
        // 获取指定天的时间戳   前面传负数
        var someDay = new Date(today.getTime() + oneDay*n)
        // 将指定天的时分秒设为我们指定的值
        someDay.setHours(Number(timeArr[0]))
        someDay.setMinutes(Number(timeArr[1]))
        today.setSeconds(Number(timeArr[2]));
        someDay.setMilliseconds(0);
        return someDay
    }
 
    console.log(someDaySomeTime(-2, '10/20/30'))