js獲取7天之前的日期方法

   //日期計算
    function getBeforeDate(n) {
        var n = n;
        var d = new Date();
        var year = d.getFullYear();
        var mon = d.getMonth() + 1;
        var day = d.getDate();
        if(day <= n) {
            if(mon > 1) {
                mon = mon - 1;
            } else {
                year = year - 1;
                mon = 12;
            }
        }
        d.setDate(d.getDate() - n);
        year = d.getFullYear();
        mon = d.getMonth() + 1;
        day = d.getDate();
        // s = year + "-" + (mon < 10 ? ('0' + mon) : mon) + "-" + (day < 10 ? ('0' + day) : day);
        // s =(mon < 10 ? ('0' + mon) : mon) + "-" + (day < 10 ? ('0' + day) : day);
        s = mon+"月"+day+"日";
        return s;
    }

獲取年月

function getBeforeYearDate(n) {
        var n = n;
        var d = new Date();
        var year = d.getFullYear();
        var mon = d.getMonth() + 1;
        var day = d.getDate();
        if(day <= n) {
            if(mon > 1) {
                mon = mon - 1;
            } else {
                year = year - 1;
                mon = 12;
            }
        }
        d.setDate(d.getDate() - n);
        year = d.getFullYear();
        mon = d.getMonth() + 1;
        day = d.getDate();
        // s = year + "-" + (mon < 10 ? ('0' + mon) : mon) + "-" + (day < 10 ? ('0' + day) : day);
        // s =(mon < 10 ? ('0' + mon) : mon) + "-" + (day < 10 ? ('0' + day) : day);
        s = year+"年"+mon+"月";
        return s;
    }