September 2022
Intermediate to advanced
585 pages
8h 17m
Chinese
Content preview from JavaScript 经典实例：第三版
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日期
｜
99
271,821
年），也可以表示遥远的未来（公元
275,760
年）。
调用
Date.getTime()
方法可以获取毫秒数。
两个
Date
对象仅当完全一致时才相等，一直延续到毫秒。两个表示同一日期的
Date
对象，如果时间部分不同，也是不相等的。这可能导致问题，因为你可能并不
知道
Date
对象包含时间信息。创建表示今天的
Date
对象（
4.1
节）时经常遇到这
个问题。
为了避免这个问题，可以使用
Date.setHours()
方法去掉时间信息。不要被这个方
法的名称迷惑了，其实它最多可以接受四个参数，分别设定时分秒和毫秒。如果想
创建一个只含日期的
Date
对象，把这些组成部分都设为
0
。
const
today =
new
Date();
//
再为当前日期创建一个副本
//
日期没变，但是时间可能已经走到下一毫秒了
const
todayDifferent =
new
Date();
//
可能为真，也可能为假，取决于超出你控制的计时因素
console.log(today.getTime() === todayDifferent.getTime());
//
去掉所有时间信息
todayDifferent.setHours(0,0,0,0);
today.setHours(0,0,0,0);
//
始终为真，因为两个实例的时间都去掉了
console.log(today.getTime() === todayDifferent.getTime());
4.4.4
参考
关于日期的更多数学运算，见
4.5
节和
4.3 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.