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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96
｜
第
4
章
日（换言之，如果把日设为
40
，
JavaScript
直接把日期延到下一个月）。
Date
构造
函数还接受在不同的计算机中解析结果不一致的字符串。
如果使用非数字字符串创建
Date
对象，得到的是一个“
Invalid Date
”（无效日期）
对象。这种情况可以使用
isNaN()
方法检查。
const
badDate = '12 bananas';
const
convertedDate =
new
Date(badDate);
if (Number.isNaN(convertedDate)) {
//
代码执行到这里，因为没有成功创建日期对象
}
else
{
//
如果是有效的
Date
实例，代码执行到这里
}
之所以可以这样检查，是因为
Date
对象的背后其实是数字，详见
4.4
节。
4.2.4
参考
4.6
节说明反向操作，即把
Date
对象转换成字符串。
4.3
在日期上增加天数
4.3.1
问题
你想计算在某个日期之前或之后一定天数的日期。
4.3.2
方案
使用
Date.getDate()
方法获取当前日期是一个月中的第几天，然后使用
Date.
setDate()
方法修改。
Date
对
象足够聪明，如有必要，会顺延到下个月或下一年。
const
today =
new
Date();
const
currentDay = today.getDate();
//
三周后的日期是什么？
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