javscript获取本月的开始日期和结束日期（包括上个月、下个月）

代码封装：

function getMonth(type, months) {
  var d = new Date();
  var year = d.getFullYear();
  var month = d.getMonth() + 1;
  if (Math.abs(months) > 12) {
    months = months % 12;
  };
  if (months != 0) {
    if (month + months > 12) {
      year++;
      month = (month + months) % 12;
    } else if (month + months < 1) {
      year--;
      month = 12 + month + months;
    } else {
      month = month + months;
    };
  };
  month = month < 10 ? "0" + month: month;
  var date = d.getDate();
  var firstday = year + "-" + month + "-" + "01";
  var lastday = "";
  if (month == "01" || month == "03" || month == "05" || month == "07" || month == "08" || month == "10" || month == "12") {
    lastday = year + "-" + month + "-" + 31;
  } else if (month == "02") {
    if ((year % 4 == 0 && year % 100 != 0) || (year % 100 == 0 && year % 400 == 0)) {
        lastday = year + "-" + month + "-" + 29;
    } else {
        lastday = year + "-" + month + "-" + 28;
    };
  } else {
    lastday = year + "-" + month + "-" + 30;
  };
  var day = "";
  if (type == "s") {
    day = firstday;
  } else {
    day = lastday;
  };
  return day;
};

调用方法：

console.log('获取月开始日期：', getMonth('s',0))
console.log('获取月结束日期：', getMonth('e',0))

//下个月
getMonday("s",1)
getMonday("e",1)