JavaScript 获取最近几周的开始时间和结束时间

首先获取最近几周 例如获取最近三周

 /**获取周 */
    getBeforeWeeksTime(num) {
        /**获取到当前的年月日 */
        var now = new Date();
        var year = now.getFullYear();       //年
        var month = now.getMonth() + 1;     //月
        var day = now.getDate();            //日
        let currentYear = year.toString();
        let currentMonth = ''
        if (month < 10)
            currentMonth += "0";
        currentMonth += month
        let currentDay = ''
        if (day < 10)
            currentDay += "0";
        currentDay += day;

        var nowDate = new Date(year, parseInt(month) - 1, day);   //获取到今天的时间
        var startDate = new Date(year, 0, 1);  //获取到今年第一月第一天
        let d = Math.round((nowDate.valueOf() - startDate.valueOf()) / 86400000); // d是当前日期是今年第多少天 
        //用d + 当前年的第一天的周差距的和在除以7就是本年第几周  
        let currentWeek = year + '-' + (Math.ceil((d + (startDate.getDay() + 1 - 1)) / 7) + 1 - num)   //获取到最近num周是第几周
        console.log('currentWeek', currentWeek);

        let weekNo = currentWeek.split("-")[1]; //获取想要计算的周是一年的第多少周
        let oneday = new Date(year + "-01-01").getDay();// 此年1号是星期几


        // 方便计算，当为星期天时为7
        if (oneday == 0) {
            oneday = 7;
        }
        let one_fistday;
        let one_lastday;
        // 如果1号刚好是星期一
        if (oneday == 1) {
            one_fistday = year + "-01-01";
            one_lastday = year + "-01-07";
        } else {
            let jj = 8 - oneday;
            one_fistday = year - 1 + "-12-" + (31 - oneday + 2 > 9 ? 31 - oneday + 2 : "0" + (31 - oneday + 2));
            one_lastday = year + "-01-" + (jj > 9 ? jj : "0" + jj);
        }

        let fistday;
        let lastday;
        // 如果刚好是第一周
        if (weekNo == 1) {
            fistday = one_fistday;
            lastday = one_lastday;
        } else {
            fistday = this.addDate(one_lastday, (weekNo - 2) * 7 + 1);
            lastday = this.addDate(one_lastday, (weekNo - 1) * 7);
        }
        let obj = {
            beforeMonday: fistday,
            beforeSunday: lastday,
        }
        return obj;
        /**
         * fistday 为前第几周的周一 格式(xxxx-xx-xx)
         * lastday 为前第几周的周日 格式(xxxx-xx-xx)
         */
    },
    addDate(date, days) {
        var d = new Date(date);
        d.setDate(d.getDate() + days);
        var m = d.getMonth() + 1;

        return (
            d.getFullYear() +
            "-" +
            (m > 9 ? m : "0" + m) +
            "-" +
            (d.getDate() > 9 ? d.getDate() : "0" + d.getDate())
        );
    },

获取本周的最后一天 ：

 /**获取本周最后一天 */
    getLastWeek() {
        let lastTime = new Date(new Date().getTime() + 3600 * 1000 * 24 * (7 - new Date().getDay()));
        let date = new Date(lastTime)
        let y = date.getFullYear()
        let m = date.getMonth() + 1
        m = m < 10 ? '0' + m : m
        let d = date.getDate()
        d = d < 10 ? '0' + d : d
        let resTime = y + '-' + m + '-' + d
        return resTime
    },