js 时间处理

let date = new Date(), y = date.getFullYear(), m = date.getMonth(),d = date.getDate();
let firstDay = new Date(y, m, 1); //获取当前月的第1天
let lastDay = new Date(y, m + 1, 0); //获取当前月的最后1天
let nextMonth = new Date(y, m + 1, d) //获取下个月
let nextMonth = new Date(y, m - 1, d) //获取上个月

取指定日期的上个月

var now = new Date("2015-08-08");//指定日期2015-08-8的上个月
console.log(now);
var lastMonth = new Date(now.getFullYear(),now.getMonth()-1,now.getDate());//上个月
console.log(lastMonth)