javascript 未定义时刻 vs 空时刻
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Moment of undefined vs moment of null
提问by rishat
If wonder why
如果想知道为什么
> moment(undefined).isBefore()
true
but
但
> moment(null).isBefore()
false
Is there any rational explanation for this behavior?
这种行为有什么合理的解释吗？
回答by Brian
moment(undefined)is equivalent to moment(), which assumes the initial state to be the current date/time.
moment(undefined)等价于moment()，它假定初始状态为当前日期/时间。
moment(null), on the other hand, is not a thing. It is not valid (at least not in the version I'm playing with), and has undocumented results.
moment(null)，另一方面，不是一回事。它无效（至少不在我正在使用的版本中），并且具有未记录的结果。
Of course, you can read the source code, and find that isBeforedoesn't check for undefinedeither. In other words, momentjs is not expecting itself to be used this way, twice.
当然，您可以阅读源代码，并发现它们isBefore都没有检查undefined。换句话说，momentjs 并不期望自己以这种方式被使用两次。
