blocks|key|1467228|text|​|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467229|function+daysInMonth+(month,+year)+{+//+Use+1+for+January,+2+for+February,+etc.
++return+new+Date(year,+month,+0).getDate();
}

console.log(daysInMonth(2,+1999));+//+February+in+a+non-leap+year.
console.log(daysInMonth(2,+2000));+//+February+in+a+leap+year.|code-block|syntax|javascript|1467230|1467231|第0天是上个月的最后一天。因为month构造函数是从0开始的，所以它工作得很好。这是一个小技巧，但这基本上就是你减去32的结果。|1467232|更多信息请访问：Number+of+days+in+the+current+month|offset|length|1467233|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/69267613/7942242^0|0|0|0|0|8|Z|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Y|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|Z|8|@]|9|@$L|10|M|11|1|12]]|A|$]]|$1|N|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]]]

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function daysInMonth (month, year) { // Use 1 for January, 2 for February, etc.
  return new Date(year, month, 0).getDate();
}

console.log(daysInMonth(2, 1999)); // February in a non-leap year.
console.log(daysInMonth(2, 2000)); // February in a leap year.</code></pre>
</div>
</div>
</p>
<p>Day 0 is the last day in the previous month. Because the month constructor is 0-based, this works nicely. A bit of a hack, but that's basically what you're doing by subtracting 32.</p>
<p>See more :
<a href="https://stackoverflow.com/a/69267613/7942242">Number of days in the current month</a></p>


blocks|key|1682615|text|如果您经常调用此函数，则缓存该值以获得更好的性能可能很有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1682616|以下是FlySwat's+answer的缓存版本|offset|length|1682617|var+daysInMonth+=+(function()+{
++++var+cache+=+{};
++++return+function(month,+year)+{
++++++++var+entry+=+year+%2B+'-'+%2B+month;

++++++++if+(cache[entry])+return+cache[entry];

++++++++return+cache[entry]+=+new+Date(year,+month,+0).getDate();
++++}
})();|code-block|syntax|javascript|1682618|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/315760/what-is-the-best-way-to-determine-the-number-of-days-in-a-month-with-javascript#315767^0|0|3|G|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@$D|U|E|V|1|W]]|A|$]]|$1|F|3|G|5|H|7|X|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

<p>If you call this function often, it may be useful to cache the value for better performance.</p>

<p>Here is caching version of <a href="https://stackoverflow.com/questions/315760/what-is-the-best-way-to-determine-the-number-of-days-in-a-month-with-javascript#315767">FlySwat's answer</a>:</p>

<pre><code>var daysInMonth = (function() {
    var cache = {};
    return function(month, year) {
        var entry = year + '-' + month;

        if (cache[entry]) return cache[entry];

        return cache[entry] = new Date(year, month, 0).getDate();
    }
})();
</code></pre>


blocks|key|1467392|text|为了消除混淆，我可能会将月份字符串设置为基于，因为它当前是从0开始的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467393|function+daysInMonth(month,year)+{
++++monthNum+=++new+Date(Date.parse(month+%2B"+1,"%2Byear)).getMonth()%2B1
++++return+new+Date(year,+monthNum,+0).getDate();
}

daysInMonth('feb',+2015)
//28

daysInMonth('feb',+2008)
//29|code-block|syntax|javascript|1467394|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|$]]

<p>To take away confusion I would probably make the month string based as it is currently 0 based.</p>
<pre><code>function daysInMonth(month,year) {
    monthNum =  new Date(Date.parse(month +&quot; 1,&quot;+year)).getMonth()+1
    return new Date(year, monthNum, 0).getDate();
}

daysInMonth('feb', 2015)
//28

daysInMonth('feb', 2008)
//29
</code></pre>


blocks|key|1682727|text|对于moment.js，您可以使用daysInMonth()方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1682728|moment().daysInMonth();+//+number+of+days+in+the+current+month
moment("2012-02",+"YYYY-MM").daysInMonth()+//+29
moment("2012-01",+"YYYY-MM").daysInMonth()+//+31|code-block|syntax|javascript|1682729|entityMap|0|LINK|mutability|MUTABLE|url|http://momentjs.com/^0|2|9|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

<p>With <a href="http://momentjs.com/" rel="nofollow">moment.js</a> you can use daysInMonth() method:</p>

<pre><code>moment().daysInMonth(); // number of days in the current month
moment("2012-02", "YYYY-MM").daysInMonth() // 29
moment("2012-01", "YYYY-MM").daysInMonth() // 31
</code></pre>


blocks|key|1467642|text|这就是开始|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467643|new+Date(2019,2,0).getDate();+//28
new+Date(2020,2,0).getDate();+//29|code-block|syntax|javascript|1467644|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|$]]

<p>Here is goes</p>

<pre><code>new Date(2019,2,0).getDate(); //28
new Date(2020,2,0).getDate(); //29
</code></pre>


blocks|key|1467781|text|ES6语法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467782|const+d+=+(y,+m)+=>+new+Date(y,+m,+0).getDate();|code-block|syntax|javascript|1467783|返回|1467784|console.log(+d(2020,+2)+);
//+29

console.log(+d(2020,+6)+);
//+30|1467785|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|$]]

<p>ES6 syntax</p>

<pre><code>const d = (y, m) =&gt; new Date(y, m, 0).getDate();
</code></pre>

<p>returns</p>

<pre><code>console.log( d(2020, 2) );
// 29

console.log( d(2020, 6) );
// 30
</code></pre>


blocks|key|1467293|text|function+numberOfDays(iMonth,+iYear)+{
+++++++++var+myDate+=+new+Date(iYear,+iMonth+%2B+1,+1);++//find+the+fist+day+of+next+month
+++++++++var+newDate+=+new+Date(myDate+-+1);++//find+the+last+day
++++++++++++return+newDate.getDate();+++++++++//return+#+of+days+in+this+month
++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1467294|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>function numberOfDays(iMonth, iYear) {
         var myDate = new Date(iYear, iMonth + 1, 1);  //find the fist day of next month
         var newDate = new Date(myDate - 1);  //find the last day
            return newDate.getDate();         //return # of days in this month
        }
</code></pre>


blocks|key|1467359|text|考虑到闰年：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467360|function+(year,+month)+{
++++var+isLeapYear+=+((year+%25+4+===+0+&&+year+%25+100+!==+0)+%7C%7C+year+%25+400+===+0);

++++return+[31,+(isLeapYear+?+29+:+28),+31,+30,+31,+30,+31,+31,+30,+31,+30,+31][month];
}|code-block|syntax|javascript|1467361|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|$]]

<p>Considering leap years: </p>

<pre><code>function (year, month) {
    var isLeapYear = ((year % 4 === 0 &amp;&amp; year % 100 !== 0) || year % 400 === 0);

    return [31, (isLeapYear ? 29 : 28), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month];
}
</code></pre>


blocks|key|1467517|text|单行直接计算(无Date对象)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467518|​|1467519|function+daysInMonth(m,+y)+{//m+is+1-based,+feb+=+2
+++return+31+-+(--m+%5E+1?+m+%25+7+&+1:++y+&+3?+3:+y+%25+25?+2:+y+&+15?+3:+2);
}

console.log(daysInMonth(2,+1999));+//+February+in+a+non-leap+year
console.log(daysInMonth(2,+2000));+//+February+in+a+leap+year|code-block|syntax|javascript|1467520|1467521|以0为基数的变化：|1467522|function+daysInMonth(m,+y)+{//m+is+0-based,+feb+=+1
+++return+31+-+(m+%5E+1?+m+%25+7+&+1:++y+&+3?+3:+y+%25+25?+2:+y+&+15?+3:+2);
}|1467523|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|R|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|T|8|@]|9|@]|A|$]]|$1|L|3|M|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|N|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|O|$]]

<p>One-liner direct computation (no Date object):</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function daysInMonth(m, y) {//m is 1-based, feb = 2
   return 31 - (--m ^ 1? m % 7 &amp; 1:  y &amp; 3? 3: y % 25? 2: y &amp; 15? 3: 2);
}

console.log(daysInMonth(2, 1999)); // February in a non-leap year
console.log(daysInMonth(2, 2000)); // February in a leap year</code></pre>
</div>
</div>
</p>

<p>Variation with 0-based months:</p>

<pre><code>function daysInMonth(m, y) {//m is 0-based, feb = 1
   return 31 - (m ^ 1? m % 7 &amp; 1:  y &amp; 3? 3: y % 25? 2: y &amp; 15? 3: 2);
}
</code></pre>


blocks|key|1682830|text|如果要计算Date对象当前月份的天数，请考虑使用以下方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1682831|Date.prototype.getNumberOfDaysInMonth+=+function(monthOffset)+{
++++if+(monthOffset+!==+undefined)+{
++++++++return+new+Date(this.getFullYear(),+this.getMonth()%2BmonthOffset,+0).getDate();
++++}+else+{
++++++++return+new+Date(this.getFullYear(),+this.getMonth(),+0).getDate();
++++}
}|code-block|syntax|javascript|1682832|然后你可以像这样运行它：|1682833|var+myDate+=+new+Date();
myDate.getNumberOfDaysInMonth();+//+Returns+28,+29,+30,+31,+etc.+as+necessary
myDate.getNumberOfDaysInMonth();+//+BONUS:+This+also+tells+you+the+number+of+days+in+past/future+months!|1682834|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|$]]

<p>If you want the number of days in the current month of a Date object, consider the following method:</p>

<pre><code>Date.prototype.getNumberOfDaysInMonth = function(monthOffset) {
    if (monthOffset !== undefined) {
        return new Date(this.getFullYear(), this.getMonth()+monthOffset, 0).getDate();
    } else {
        return new Date(this.getFullYear(), this.getMonth(), 0).getDate();
    }
}
</code></pre>

<p>Then you can run it like this:</p>

<pre><code>var myDate = new Date();
myDate.getNumberOfDaysInMonth(); // Returns 28, 29, 30, 31, etc. as necessary
myDate.getNumberOfDaysInMonth(); // BONUS: This also tells you the number of days in past/future months!
</code></pre>


blocks|key|1467559|text|在一行中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467560|//+month+is+1-12
function+getDaysInMonth(year,+month){
++++return+month+==+2+?+28+%2B+(year+%25+4+==+0+?+(year+%25+100+==+0+?+(year+%25+400+==+0+?+1+:+0)+:+1):0)+:+31+-+(month+-+1)+%25+7+%25+2;
}|code-block|syntax|javascript|1467561|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|$]]

<p>In a single line:</p>

<pre><code>// month is 1-12
function getDaysInMonth(year, month){
    return month == 2 ? 28 + (year % 4 == 0 ? (year % 100 == 0 ? (year % 400 == 0 ? 1 : 0) : 1):0) : 31 - (month - 1) % 7 % 2;
}
</code></pre>


blocks|key|1467694|text|与选择的答案相比，可能有点超过kill+:)，但它是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467695|​|1467696|function+getDayCountOfMonth(year,+month)+{
++if+(month+===+3+%7C%7C+month+===+5+%7C%7C+month+===+8+%7C%7C+month+===+10)+{
++++return+30;
++}

++if+(month+===+1)+{
++++if+(year+%25+4+===+0+&&+year+%25+100+!==+0+%7C%7C+year+%25+400+===+0)+{
++++++return+29;
++++}+else+{
++++++return+28;
++++}
++}

++return+31;
};

console.log(getDayCountOfMonth(2020,+1));|code-block|syntax|javascript|1467697|1467698|我在这里找到了上面的代码：https://github.com/ElemeFE/element/blob/dev/src/utils/date-util.js|offset|length|1467699|1467700|function+isLeapYear(year)+{+
++return+((year+%25+4+===+0+&&+year+%25+100+!==+0)+%7C%7C+year+%25+400+===+0);+
};

const+getDaysInMonth+=+function+(year,+month)+{
++return+[31,+(isLeapYear(year)+?+29+:+28),+31,+30,+31,+30,+31,+31,+30,+31,+30,+31][month];
};

console.log(getDaysInMonth(2020,+1));|1467701|1467702|我在这里找到了上面的代码：https://github.com/datejs/Datejs/blob/master/src/core.js|1467703|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/ElemeFE/element/blob/dev/src/utils/date-util.js|1|https://github.com/datejs/Datejs/blob/master/src/core.js^0|0|0|0|0|D|1U|0|0|0|0|0|D|1K|1|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|14|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|15|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|16|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|17|8|@]|9|@$L|18|M|19|1|1A]]|A|$]]|$1|N|3|C|5|6|7|1B|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|Q|3|C|5|6|7|1D|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1E|8|@]|9|@$L|1F|M|1G|1|1H]]|A|$]]|$1|T|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|U|$V|$5|W|X|Y|A|$Z|10]]|11|$5|W|X|Y|A|$Z|12]]]]

<p>May be bit over kill when compared to selected answer :) But here it is:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function getDayCountOfMonth(year, month) {
  if (month === 3 || month === 5 || month === 8 || month === 10) {
    return 30;
  }

  if (month === 1) {
    if (year % 4 === 0 &amp;&amp; year % 100 !== 0 || year % 400 === 0) {
      return 29;
    } else {
      return 28;
    }
  }

  return 31;
};

console.log(getDayCountOfMonth(2020, 1));</code></pre>
</div>
</div>
</p>

<p>I found the above code over here: <a href="https://github.com/ElemeFE/element/blob/dev/src/utils/date-util.js" rel="nofollow noreferrer">https://github.com/ElemeFE/element/blob/dev/src/utils/date-util.js</a></p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function isLeapYear(year) { 
  return ((year % 4 === 0 &amp;&amp; year % 100 !== 0) || year % 400 === 0); 
};

const getDaysInMonth = function (year, month) {
  return [31, (isLeapYear(year) ? 29 : 28), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month];
};

console.log(getDaysInMonth(2020, 1));</code></pre>
</div>
</div>
</p>

<p>I found the above code over here: <a href="https://github.com/datejs/Datejs/blob/master/src/core.js" rel="nofollow noreferrer">https://github.com/datejs/Datejs/blob/master/src/core.js</a></p>


blocks|key|1467755|text|如果您要传递一个日期变量，这可能会有所帮助|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467756|​|1467757|const+getDaysInMonth+=+date+=>
++new+Date(date.getFullYear(),+date.getMonth()+%2B+1,+0).getDate();

daysInThisMonth+=+getDaysInMonth(new+Date());

console.log(daysInThisMonth);|code-block|syntax|javascript|1467758|1467759|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

<p>If you are going to pass a date variable this may helpful</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>const getDaysInMonth = date =&gt;
  new Date(date.getFullYear(), date.getMonth() + 1, 0).getDate();

daysInThisMonth = getDaysInMonth(new Date());

console.log(daysInThisMonth);</code></pre>
</div>
</div>
</p>


blocks|key|1683052|text|一行代码，不使用Date对象：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1683053|const+countDays+=+(month,+year)+=>+30+%2B+(month+===+2+?+(year+%25+4+===+0+&&+1)+-+2+:+(month+%2B+Number(month+>+7))+%25+2);|code-block|syntax|javascript|1683054|返回：|1683055|countDays(11,2020)+//+30
countDays(2,2020)+//+29
countDays(2,2021)+//+28|1683056|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|$]]

<p>One-liner, without using Date objects:</p>
<pre><code>const countDays = (month, year) =&gt; 30 + (month === 2 ? (year % 4 === 0 &amp;&amp; 1) - 2 : (month + Number(month &gt; 7)) % 2);
</code></pre>
<p>returns:</p>
<pre><code>countDays(11,2020) // 30
countDays(2,2020) // 29
countDays(2,2021) // 28
</code></pre>


blocks|key|1467625|text|也许不是最优雅的解决方案，但易于理解和维护；而且，它经过了战斗测试。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1467626|function+daysInMonth(month,+year)+{
++++var+days;
++++switch+(month)+{
++++++++case+1:+//+Feb,+our+problem+child
++++++++++++var+leapYear+=+((year+%25+4+==+0)+&&+(year+%25+100+!=+0))+%7C%7C+(year+%25+400+==+0);
++++++++++++days+=+leapYear+?+29+:+28;
++++++++++++break;
++++++++case+3:+case+5:+case+8:+case+10:+
++++++++++++days+=+30;
++++++++++++break;
++++++++default:+
++++++++++++days+=+31;
++++++++}
++++return+days;
},|code-block|syntax|javascript|1467627|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|$]]

<p>Perhaps not the most elegant solution, but easy to understand and maintain; and, it's battle-tested.</p>

<pre><code>function daysInMonth(month, year) {
    var days;
    switch (month) {
        case 1: // Feb, our problem child
            var leapYear = ((year % 4 == 0) &amp;&amp; (year % 100 != 0)) || (year % 400 == 0);
            days = leapYear ? 29 : 28;
            break;
        case 3: case 5: case 8: case 10: 
            days = 30;
            break;
        default: 
            days = 31;
        }
    return days;
},
</code></pre>


<p>I've been using this function but I'd like to know what's the most efficient and accurate way to get it.</p>

<pre><code>function daysInMonth(iMonth, iYear) {
   return 32 - new Date(iYear, iMonth, 32).getDate();
}
</code></pre>


What is the best way to determine the number of days in a month with JavaScript?

我一直在使用这个函数，但我想知道获取它的最有效和准确的方法是什么。function daysInMonth(iMonth, iYear) {   return 32 - new Date(iYear, iMonth, 32).getDate();}

问使用JavaScript确定一个月的天数的最佳方法是什么？
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问使用JavaScript确定一个月的天数的最佳方法是什么？
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