下面是js中取得指定天数后的时间这个功能的函数代码：

/* 取得指定天数后的时间 */
function getRecentDay(day) {
  var today = new Date();
  var targetday_milliseconds = today.getTime() + 1000 * 60 * 60 * 24 * day;
  today.setTime(targetday_milliseconds);
  var tYear = today.getFullYear();
  var tMonth = today.getMonth();
  var tDate = today.getDate();
  var tHours = 23;//today.getHours();
  var tMinutes = 59;//today.getMinutes();
  var tSeconds = 59;//today.getSeconds();
  tMonth = doHandleMonth(tMonth + 1);
  tDate = doHandleMonth(tDate);
  tHours = doHandleMonth(tHours);
  tMinutes = doHandleMonth(tMinutes);
  tSeconds = doHandleMonth(tSeconds);

  return tYear + "-" + tMonth + "-" + tDate + ' ' + tHours + ':' + tMinutes + ':' + tSeconds;
}
function doHandleMonth(month) {
  var m = month;
  if (month.toString().length == 1) {
      m = "0" + month;
  }
  return m;
}