moment().isBefore(Moment|String|Number|Date|Array);
moment().isBefore(Moment|String|Number|Date|Array, String);
检查一个 moment 是否在另一个 moment 之前。 第一个参数会被解析为 moment（如果尚未解析）。
moment('2010-10-20').isBefore('2010-10-21'); // true
如果要将粒度限制为毫秒以外的单位，则将单位作为第二个参数传入。
由于第二个参数用于确定精度，且不仅仅是要检查的单个值，因此使用 day 将会检查年份、月份、日期。
moment('2010-10-20').isBefore('2010-12-31', 'year'); // false
moment('2010-10-20').isBefore('2011-01-01', 'year'); // true
与 moment#isAfter 和 moment#isSame 一样，moment#startOf 支持的任何时间单位也适用于 moment#isBefore。
year month week isoWeek day hour minute second
如果未将任何内容传给 moment#isBefore，则它将会默认为当前时间。
注意：moment().isBefore() 具有未定义的行为，且不应被使用！
如果代码运行快速，则初始创建的 moment 将会与isBefore 中创建的要执行检查的相同，因此结果将会为 false。
但是，如果代码运行速度较慢，则有可能在 isBefore 中创建的 moment 可测量地在 moment() 中创建的之后，因此该调用将会返回 true。
moment().isBefore(Moment|String|Number|Date|Array);
moment().isBefore(Moment|String|Number|Date|Array, String);
Check if a moment is before another moment. The first argument will be parsed as a moment, if not already so.
moment('2010-10-20').isBefore('2010-10-21'); // true
If you want to limit the granularity to a unit other than milliseconds, pass the units as the second parameter.
As the second parameter determines the precision, and not just a single value to check, using day will check for year, month and day.
moment('2010-10-20').isBefore('2010-12-31', 'year'); // false
moment('2010-10-20').isBefore('2011-01-01', 'year'); // true
Like moment#isAfter and moment#isSame, any of the units of time that are supported for moment#startOf are supported for moment#isBefore.
year month week isoWeek day hour minute second
If nothing is passed to moment#isBefore, it will default to the current time.
NOTE: moment().isBefore() has undefined behavior and should not be used! If
the code runs fast the initial created moment would be the same as the one
created in isBefore to perform the check, so the result would be false. But
if the code runs slower it's possible that the moment created in isBefore is
measurably after the one created in moment(), so the call would return
true.