在给定日期之前最接近的星期天使用JavaScript

问题描述

我需要知道 php & javascript

I need to know the date for last Sunday for given date in php & javascript

让我们有一个功能give_me_last_Sunday

Let's have a function give_me_last_Sunday

give_me_last_Sunday('20110517') is 20110515
give_me_last_Sunday('20110604') is 20110529

完全备份是在星期日=每周完成的。如果我要恢复每日备份，我需要全面（每周）和每日备份。我需要复制备份文件，然后恢复到临时目录，所以我恢复每日备份我需要知道每周备份文件，我需要沿日常文件复制。

The full backup is done on Sundays = weekly. If I want to restore daily backup I need full (weekly) and daily backup. I need to copy backup files before restoring to temp directory so I restoring daily backup I need to know what weekly backup file I need to copy along the daily file.

我的想法是给给定日期的朱利安表示（或类似的东西），然后减去1并检查是否是星期天...不知道这是最好的想法，以及如何将给定日期转换为可以减去的东西。

My thought was to get Julian representation (or something similar) for the given date and then subtract 1 and check if it is Sunday ... Not sure if this is the best idea and how to convert given date into something I can subtract.

推荐答案

根据托马斯的努力，提供的输入字符串完全是您指定的格式，然后：

Based on Thomas' effort, and provided the input string is exactly the format you specified, then:

function lastSunday(d) {
  var d = d.replace(/(^\d{4})(\d{2})(\d{2}$)/,'$1/$2/$3');
  d = new Date(d);
  d.setDate(d.getDate() - d.getDay());
  return d;
}

修改

如果我现在写这个，我不会依赖Date对象来解析字符串，而是自己做：

Edit

If I were to write that now, I'd not depend on the Date object parsing the string but do it myself:

function lastSunday(s) {
  var d = new Date(s.substring(0,4), s.substring(4,6) - 1, s.substring(6));
  d.setDate(d.getDate() - d.getDay());
  return d;
}

虽然所有浏览器的yyyy / mm / dd格式正确解析，我认为坚持基本的方法是更健壮的。特别是当他们可能更有效率。

While the format yyyy/mm/dd is parsed correctly by all browsers I've tested, I think it's more robust to stick to basic methods. Particularly when they are likely more efficient.

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