monthDay(year, month) {
        month = parseInt(month, 10);
        let d = new Date(year, month, 0); // 这个是都可以兼容的
        let date = new Date(year + "/" + month + "/0"); // IE浏览器可以获取天数，谷歌浏览器会返回NaN
        return d.getDate();
    }
    getNextMonth(date, length) {
        let yy = date.getFullYear();
        let mm = date.getMonth();
        let dd = date.getDate();

        let nm = 0; // 目标月份
        nm = mm + length;
        let nd = 0; // 目标天数
        if (this.monthDay(yy, nm + 1) < dd) {
            nd = this.monthDay(yy, nm + 1);
        } else {
            nd = dd - 1;
        }

        date.setDate(1);
        date.setMonth(nm);
        date.setDate(nd);
        return date;
    }

this.getNextMonth(new Date(), 2)