getBeforeDate(n) {//传入天数
var n = n;
var d = new Date();
var year = d.getFullYear();
var mon = d.getMonth() + 1;
var day = d.getDate();
if (Number(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();
var s = year + "-" + (mon < 10 ? ('0' + mon) : mon) +"-"+(day < 10 ? ('0' + day):day);
return s;
}