根据 MDN

“日期对象基于一个时间值，该时间值是自 1970 年 1 月 1 日 UTC 以来的毫秒数。”

那为什么它接受负值呢？

即使负值不应该是 1970 年 1 月 1 日之前的平均值吗？

new Date('0000', '00', '-1');   // "1899-12-30T05:00:00.000Z"
new Date('0000', '00', '00');   // "1899-12-31T05:00:00.000Z"
new Date('-9999', '99', '99');  // "-009991-07-08T04:00:00.000Z"

发生了什么事？

更新

对于一些正值，年份从1900年开始

new Date(100);                  // "1970-01-01T00:00:00.100Z"   // it says 100Z
new Date(0100);                 // "1970-01-01T00:00:00.064Z"   // it says 64Z
new Date("0006","06","06");     // "1906-07-06T04:00:00.000Z"

另请注意，在最后一个中，日期显示为 4，这是错误的。

我怀疑这是某种 Y2K 漏洞？!!

最佳答案

This is hard and inconsistent, yes. The JavaScript Date object was based on the one in Java 1.0, which is so bad that Java redesigned a whole new package. JavaScript is not so lucky.

1. 日期“基于”unix epoch因为它是怎样的defined .这是内部详细信息。
2. 1st Jan 1970 是这个基线的实际时间。
3. since 是时间戳值的方向:+ve 向前，-ve 向后。
4. 在外部，Date 构造函数有几种不同的用法，具体取决于参数:

零参数=当前时间

new Date()   // Current datetime. Every tutorial should teach this.

The time is absolute, but 'displayed' timezone may be UTC or local.

For simplicity, this answer will use only UTC. Keep timezone in mind when you test.

一个数字参数=时间戳@1970

new Date(0)    // 0ms from 1970-01-01T00:00:00Z.
new Date(100)  // 100ms from 1970 baseline.
new Date(-10)  // -10ms from 1970 baseline.

一个字符串参数= iso date string

new Date('000')        // Short years are invalid, need at least four digits.
new Date('0000')       // 0000-01-01.  Valid because there are four digits.
new Date('1900')       // 1900-01-01.
new Date('1900-01-01') // Same as above.
new Date('1900-01-01T00:00:00') // Same as above.
new Date('-000001')    // 2 BC, see below. Yes you need all those zeros.

两个或多个参数=年、月等@1900或0000

new Date(0,0)      // 1900-01-01T00:00:00Z.
new Date(0,0,1)    // Same as above.  Date is 1 based.
new Date(0,0,0)    // 1 day before 1900 = 1899-12-31.
new Date(0,-1)     // 1 month before 1900 = 1899-12-01.
new Date(0,-1,0)   // 1 month and 1 day before 1900 = 1899-11-30.
new Date(0,-1,-1)  // 1 month and *2* days before 1900 = 1899-11-29.
new Date('0','1')  // 1900-02-01. Two+ params always cast to year and month.
new Date(100,0)    // 0100-01-01. Year > 99 use year 0 not 1900.
new Date(1900,0)   // 1900-01-01. Same as new Date(0,0). So intuitive!

负年份 = BC

new Date(-1,0)    // 1 year before 0000-01-01 = 1 year before 1 BC = 2 BC.
new Date(-1,0,-1) // 2 days before 2 BC.  Fun, yes?  I'll leave this as an exercise.

There is no 0 AC. There is 1 AC and the year before it is 1 BC. Year 0 is 1 BC by convention.

2 BC is displayed as year "-000001". The extra zeros are required because it is outside normal range (0000 to 9999). If you new Date(12345,0) you will get "+012345-01-01", too.

Of course, the Gregorian calendar, adopted as late as 1923 in Europe, will cease to be meaningful long before we reach BC. In fact, scholars accept that Jesus wasn't born in 1 BC. But with the stars and the land moving at this scale, calendar is the least of your worries.

剩下的给定代码只是这些情况的变体。例如:

new Date(0100)          // One number = epoch. 0100 (octal) = 64ms since 1970
new Date('0100')        // One string = iso = 0100-01-01.
new Date(-9999, 99, 99) // 9999 years before BC 1 and then add 99 months and 98 days

希望您玩得开心。请不要忘记投票。 :)

To stay sane, keep all dates in ISO 8601 and use the string constructor.
And if you need to handle timezone, keep all datetimes in UTC.

关于javascript - 为什么 Date 接受负值？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/41340836/