javascript寻找闰年 [英] javascript to find leap year
问题描述
当我有一个月的二月时,如何获得下面的代码?目前正在到达这一天,然后停下来,才能确定是否是一个闰年。
How can I get the code below to work when I have a month of february? Currently it is getting to the day and then stopping before getting to the if to determine whether it is a leap year.
if (month == 2) {
if (day == 29) {
if (year % 4 != 0 || year % 100 == 0 && year % 400 != 0) {
field.focus();
field.value = month +'/' + '';
}
}
else if (day > 28) {
field.focus();
field.value = month +'/' + '';
}
}
推荐答案
使用日期对象更安全的日期时间内容,例如
It's safer to use Date objects for datetime stuff, e.g.
isLeap = new Date(year, 1, 29).getMonth() == 1
由于人们不断询问这是如何工作的,它与JS如何计算年月日的日期值(详情这里)。基本上,它首先计算一个月的第一个月,然后添加N -1天。所以当我们在非闰年要求2月29日,结果将是2月1日+ 28日= 3月1日:
Since people keep asking about how exactly this works, it has to do with how JS calculates the date value from year-month-day (details here). Basically, it first calculates the first of the month and then adds N -1 days to it. So when we're asking for the 29th Feb on a non-leap year, the result will be the 1st Feb + 28 days = 1st March:
> new Date(2015, 1, 29)
< Sun Mar 01 2015 00:00:00 GMT+0100 (CET)
在闰年, 1 + 28 = 2月29日:
On a leap year, the 1st + 28 = 29th Feb:
> new Date(2016, 1, 29)
< Mon Feb 29 2016 00:00:00 GMT+0100 (CET)
在上面的代码中将日期设置为2月29日,并查看是否发生翻滚。如果没有(月份还是1,即2月),这是一个闰年,否则是一个非飞跃的一个。
In the code above, I set the date to 29th Feb and look if a roll-over took place. If not (the month is still 1, i.e. February), this is a leap year, otherwise a non-leap one.
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