let currentDate = "2019-04";
currentDate = new Date(currentDate); // 将日期格式转换为 Mon Apr 01 2019 08:00:00 GMT+0800 (中国标准时间)
// 月份加一
let lastDate = currentDate.setMonth(currentDate.getMonth() - 1); // 输出日期格式为毫秒形式1551398400000
lastDate = new Date(lastDate);
let lastYear = lastDate.getFullYear();
let lastMonth = checkMonth(lastDate.getMonth() + 1); // 因日期中的月份表示为0-11，所以要显示正确的月份，需要 + 1
lastDate = lastYear + ‘-‘ + lastMonth; // "2019-03"
// 月份减一
let nextDate = currentDate.setMonth(currentDate.getMonth() + 1); // 输出日期格式为毫秒形式1556668800000
nextDate = new Date(nextDate);
let nextYear = nextDate.getFullYear();
let nextMonth = checkMonth(nextDate.getMonth() + 1); // 因日期中的月份表示为0-11，所以要显示正确的月份，需要 + 1
nextDate = nextYear + ‘-‘ + nextMonth; // "2019-05"
