blocks|key|1122351|text|对象配置的一行代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1122352|new+Date(new+Date().setHours(0,0,0,0));|code-block|syntax|javascript|1122353|创建元素时：|1122354|dateFieldConfig+=+{
++++++name:+"mydate",
++++++value:+new+Date(new+Date().setHours(0,+0,+0,+0)),
}|1122355|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

A one-liner for object configs:

<pre><code>new Date(new Date().setHours(0,0,0,0));
</code></pre>

When creating an element:

<pre><code>dateFieldConfig = {
 name: "mydate",
 value: new Date(new Date().setHours(0, 0, 0, 0)),
}
</code></pre>

blocks|key|1122425|text|之所以要在这里添加这一点，是因为我登录到了这个页面，正在寻找如何在moment.js中做到这一点，其他人也可能会这样做。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1122426|[理由："moment“这个词已经出现在这个页面的其他地方，所以搜索引擎直接指向这里，而moment.js的普及程度足以保证它在其他与日期相关的so问题中被提及的频率。]|1122427|因此，在2.0.0及更高版本中：|1122428|date.startOf('day');|code-block|syntax|javascript|1122429|对于早期版本：|1122430|date.sod();|1122431|文档：|1122432|http://momentjs.com/docs/#/manipulating/start-of/|1122433|entityMap|0|LINK|mutability|MUTABLE|url|http://momentjs.com/|1|2^0|X|9|0|0|18|9|1|0|0|0|0|0|0|0|1D|2|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@$A|15|B|16|1|17]]|C|$]]|$1|D|3|E|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]]|C|$]]|$1|F|3|G|5|6|7|1C|8|@]|9|@]|C|$]]|$1|H|3|I|5|J|7|1D|8|@]|9|@]|C|$K|L]]|$1|M|3|N|5|6|7|1E|8|@]|9|@]|C|$]]|$1|O|3|P|5|J|7|1F|8|@]|9|@]|C|$K|L]]|$1|Q|3|R|5|6|7|1G|8|@]|9|@]|C|$]]|$1|S|3|T|5|6|7|1H|8|@]|9|@$A|1I|B|1J|1|1K]]|C|$]]|$1|U|3|-4|5|6|7|1L|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]|12|$5|X|Y|Z|C|$10|11]]|13|$5|X|Y|Z|C|$10|T]]]]

Just going to add this here because I landed on this page looking for how to do this in <a href="http://momentjs.com/">moment.js</a> and others may do too. 

[Rationale: the word "moment" already appears elsewhere on this page so search engines direct here, and <a href="http://momentjs.com/">moment.js</a> is widespread enough to warrant to being covered going on how often it is mentioned in other date-related SO questions]

So, in version 2.0.0 and above:

<pre><code>date.startOf('day');
</code></pre>

For earlier versions:

<pre><code>date.sod();
</code></pre>

Docs:

<a href="http://momentjs.com/docs/#/manipulating/start-of/">http://momentjs.com/docs/#/manipulating/start-of/</a>

blocks|key|1122444|text|您可能可以使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1122445|new+Date().setUTCHours(0,0,0,0)|code-block|syntax|javascript|1122446|如果您只需要该值一次。|1122447|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You can probably use 

<pre><code>new Date().setUTCHours(0,0,0,0)
</code></pre>

if you need the value only once.

blocks|key|1122533|text|如果用日期计算，夏季通常会导致午夜(CEST)多一小时或少一小时。当日期返回时，这会导致1天的差异。因此，日期必须舍入到最近的午夜。因此，代码将是(+to+To+jamisOn)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1122534|++++var+d+=+new+Date();
++++if(d.getHours()+<+12)+{
++++d.setHours(0,0,0,0);+//+previous+midnight+day
++++}+else+{
++++d.setHours(24,0,0,0);+//+next+midnight+day
++++}|code-block|syntax|javascript|1122535|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If calculating with dates summertime will cause often 1 uur more or one hour less than midnight (CEST). This causes 1 day difference when dates return. So the dates have to round to the nearest midnight. So the code will be (ths to jamisOn):

<pre><code> var d = new Date();
 if(d.getHours() &lt; 12) {
 d.setHours(0,0,0,0); // previous midnight day
 } else {
 d.setHours(24,0,0,0); // next midnight day
 }
</code></pre>

blocks|key|1122318|text|给@Dan的例子增加了用处，我需要找到下一个中午或午夜。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1122319|var+d+=+new+Date();
if(d.getHours()+<+12)+{
+++d.setHours(12,0,0,0);+//+next+midnight/midday+is+midday
}+else+{
+++d.setHours(24,0,0,0);+//+next+midnight/midday+is+midnight
}|code-block|syntax|javascript|1122320|这允许我为事件设置频率上限，只允许任何访问我网站的访问者在上午和下午发生一次。捕获的日期用于设置cookie的过期时间。|1122321|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Adding usefulness to @Dan's example, I had the need to find the next midday or midnight.

<pre><code>var d = new Date();
if(d.getHours() &lt; 12) {
 d.setHours(12,0,0,0); // next midnight/midday is midday
} else {
 d.setHours(24,0,0,0); // next midnight/midday is midnight
}
</code></pre>

This allowed me to set a frequency cap for an event, only allowing it to happen once in the morning and once in the afternoon for any visitor to my site. The date captured was used to set the expiration of the cookie.

blocks|key|907712|text|我已经做了几个原型来为我处理这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|907713|//+This+is+a+safety+check+to+make+sure+the+prototype+is+not+already+defined.
Function.prototype.method+=+function+(name,+func)+{
++++if+(!this.prototype[name])+{
++++++++this.prototype[name]+=+func;
++++++++return+this;
++++}
};

Date.method('endOfDay',+function+()+{
++++var+date+=+new+Date(this);
++++date.setHours(23,+59,+59,+999);
++++return+date;
});

Date.method('startOfDay',+function+()+{
++++var+date+=+new+Date(this);
++++date.setHours(0,+0,+0,+0);
++++return+date;
});|code-block|syntax|javascript|907714|如果你不想要安全检查，那么你可以使用|907715|Date.prototype.startOfDay+=+function(){
++/*Method+body+here*/
};|907716|示例用法：|907717|var+date+=+new+Date($.now());+//+$.now()+requires+jQuery
console.log('startOfDay:+'+%2B+date.startOfDay());
console.log('endOfDay:+'+%2B+date.endOfDay());|907718|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I have made a couple prototypes to handle this for me.

<pre><code>// This is a safety check to make sure the prototype is not already defined.
Function.prototype.method = function (name, func) {
 if (!this.prototype[name]) {
 this.prototype[name] = func;
 return this;
 }
};

Date.method('endOfDay', function () {
 var date = new Date(this);
 date.setHours(23, 59, 59, 999);
 return date;
});

Date.method('startOfDay', function () {
 var date = new Date(this);
 date.setHours(0, 0, 0, 0);
 return date;
});
</code></pre>

if you dont want the saftey check, then you can just use

<pre><code>Date.prototype.startOfDay = function(){
 /*Method body here*/
};
</code></pre>

Example usage:

<pre><code>var date = new Date($.now()); // $.now() requires jQuery
console.log('startOfDay: ' + date.startOfDay());
console.log('endOfDay: ' + date.endOfDay());
</code></pre>

blocks|key|907678|text|如果项目中已经有d3.js作为依赖项，或者不介意引入D3.js，d3-time+(d3.js+library+is+modular+as+of+v4.0.0)已经有了Intervals。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|907679|在将日期设置为“默认值”时，例如午夜、0.00秒、月初等，它们可能会被证明是有用的。|907680|var+d+=+new+Date();+//+Wed+Aug+02+2017+15:01:07+GMT%2B0200+(CEST)
d3.timeHour(d)+//+Wed+Aug+02+2017+00:00:00+GMT%2B0200+(CEST)
d3.timeMonth(d)+//+Tue+Aug+01+2017+00:00:00+GMT%2B0200+(CEST)|code-block|syntax|javascript|907681|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/d3/d3-time|1|https://github.com/d3/d3/releases/tag/v4.0.0|2|https://github.com/d3/d3-time#intervals^0|W|7|0|15|11|1|2B|9|2|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]|$A|10|B|11|1|12]|$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|6|7|16|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|17|8|@]|9|@]|C|$I|J]]|$1|K|3|-4|5|6|7|18|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]|U|$5|N|O|P|C|$Q|V]]]]

In case you already have d3.js as a dependency in your project, or don't mind bringing it in, <a href="https://github.com/d3/d3-time" rel="nofollow noreferrer">d3-time</a> (<a href="https://github.com/d3/d3/releases/tag/v4.0.0" rel="nofollow noreferrer">d3.js library is modular as of v4.0.0</a>) has got <a href="https://github.com/d3/d3-time#intervals" rel="nofollow noreferrer">Intervals</a>. 

They might prove useful when setting dates to "default" values, e.g. midnight, 0.00 seconds, the first of the month, etc. 

<pre><code>var d = new Date(); // Wed Aug 02 2017 15:01:07 GMT+0200 (CEST)
d3.timeHour(d) // Wed Aug 02 2017 00:00:00 GMT+0200 (CEST)
d3.timeMonth(d) // Tue Aug 01 2017 00:00:00 GMT+0200 (CEST)
</code></pre>

What is the simplest way to obtain an instance of new Date() but set the time at midnight?

What is the best way to initialize a JavaScript Date to midnight?

jQuery

获取new Date()的实例但将时间设置为午夜的最简单方法是什么？

问将JavaScript日期初始化为午夜的最佳方法是什么？
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回答 7

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