js 计算前一天或几天的日期，以及后一天或几天的日期

代码

function getDay(day) {
  var today = new Date();

  var targetday_milliseconds = today.getTime() + 1000 * 60 * 60 * 24 * day;

  today.setTime(targetday_milliseconds); //注意，这行是关键代码

  var tYear = today.getFullYear();
  var tMonth = today.getMonth();
  var tDate = today.getDate();
  tMonth = doHandleMonth(tMonth + 1);
  tDate = doHandleMonth(tDate);
  return tYear + "-" + tMonth + "-" + tDate;
}

function doHandleMonth(month) {
  var m = month;
  if (month.toString().length == 1) {
    m = "0" + month;
  }
  return m;
}

使用

后一天 getDay(1)   返回 2023-02-11
前一天 getDay(-1)   返回 2023-02-09