关于javascript:js如何获取上个月第一天和最后一天

var nowdays = new Date();var year = nowdays.getFullYear();var month = nowdays.getMonth();if (month == 0) {    month = 12;    year = year - 1;}if (month < 10) {    month = '0' + month;}var myDate = new Date(year, month, 0);var startDate = year + '-' + month + '-01 00:00:00'; //上个月第一天var endDate = year + '-' + month + '-' + myDate.getDate() + ' 23:59:00'; //上个月最初一天