What is the best way to determine the number of days in a month with JavaScript?
JavascriptDateJavascript Problem Overview
I've been using this function but I'd like to know what's the most efficient and accurate way to get it.
function daysInMonth(iMonth, iYear) {
return 32 - new Date(iYear, iMonth, 32).getDate();
}
Javascript Solutions
Solution 1 - Javascript
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.
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.
See more : Number of days in the current month
Solution 2 - Javascript
Some answers (also on other questions) had leap-year problems or used the Date-object. Although javascript's Date object covers approximately 285616 years (100,000,000 days) on either side of January 1 1970, I was fed up with all kinds of unexpected date inconsistencies across different browsers (most notably year 0 to 99). I was also curious how to calculate it.
So I wrote a simple and above all, small algorithm to calculate the correct (Proleptic Gregorian / Astronomical / ISO 8601:2004 (clause 4.3.2.1), so year 0 exists and is a leap year and negative years are supported) number of day's for a given month and year.
It uses the short-circuit bitmask-modulo leapYear algorithm (slightly modified for js) and common mod-8 month algorithm.
Note that in AD/BC notation, year 0 AD/BC does not exist: instead year 1 BC is the leap-year!
IF you need to account for BC notation then simply subtract one year of the (otherwise positive) year-value first!! (Or subtract the year from 1 for further year-calculations.)
function daysInMonth(m, y){
return m===2?y&3||!(y%25)&&y&15?28:29:30+(m+(m>>3)&1);
}
<!-- example for the snippet -->
<input type="text" value="enter year" onblur="
for( var r='', i=0, y=+this.value
; 12>i++
; r+= 'Month: ' + i + ' has ' + daysInMonth(i, y) + ' days<br>'
);
this.nextSibling.innerHTML=r;
" /><div></div>
Note, months must be 1-based!
Note, this is a different algorithm then the magic number lookup I used in my Javascript calculate the day of the year (1 - 366) answer, because here the extra branch for the leap-year is only needed for February.
Solution 3 - Javascript
If you call this function often, it may be useful to cache the value for better performance.
Here is caching version of FlySwat's answer:
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();
}
})();
Solution 4 - Javascript
To take away confusion I would probably make the month string based as it is currently 0 based.
function daysInMonth(month,year) {
var monthNum = new Date(Date.parse(month +" 1,"+year)).getMonth()+1
return new Date(year, monthNum, 0).getDate();
}
daysInMonth('feb', 2015)
//28
daysInMonth('feb', 2008)
//29
Solution 5 - Javascript
With moment.js you can use daysInMonth() method:
moment().daysInMonth(); // number of days in the current month
moment("2012-02", "YYYY-MM").daysInMonth() // 29
moment("2012-01", "YYYY-MM").daysInMonth() // 31
Solution 6 - Javascript
Here is goes
new Date(2019,2,0).getDate(); //28
new Date(2020,2,0).getDate(); //29
Solution 7 - Javascript
ES6 syntax
const d = (y, m) => new Date(y, m, 0).getDate();
returns
console.log( d(2020, 2) );
// 29
console.log( d(2020, 6) );
// 30
Solution 8 - Javascript
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
}
Solution 9 - Javascript
Considering leap years:
function (year, month) {
var isLeapYear = ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0);
return [31, (isLeapYear ? 29 : 28), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month];
}
Solution 10 - Javascript
One-liner direct computation (no Date object):
//m is 1-based, feb = 2
function daysInMonth(m,y){
return 31-(--m?y&3?3:y%25?2:y&15?3:2:m%7&1);
}
console.log(daysInMonth(2, 1999)); // February in a non-leap year
console.log(daysInMonth(2, 2000)); // February in a leap year
Solution 11 - Javascript
If you want the number of days in the current month of a Date object, consider the following method:
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();
}
}
Then you can run it like this:
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!
Solution 12 - Javascript
In a single line:
// 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;
}
Solution 13 - Javascript
May be bit over kill when compared to selected answer :) But here it is:
function getDayCountOfMonth(year, month) {
if (month === 3 || month === 5 || month === 8 || month === 10) {
return 30;
}
if (month === 1) {
if (year % 4 === 0 && year % 100 !== 0 || year % 400 === 0) {
return 29;
} else {
return 28;
}
}
return 31;
};
console.log(getDayCountOfMonth(2020, 1));
I found the above code over here: https://github.com/ElemeFE/element/blob/dev/src/utils/date-util.js
function isLeapYear(year) {
return ((year % 4 === 0 && 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));
I found the above code over here: https://github.com/datejs/Datejs/blob/master/src/core.js
Solution 14 - Javascript
If you are going to pass a date variable this may helpful
const getDaysInMonth = date =>
new Date(date.getFullYear(), date.getMonth() + 1, 0).getDate();
daysInThisMonth = getDaysInMonth(new Date());
console.log(daysInThisMonth);
Solution 15 - Javascript
One-liner, without using Date objects:
const countDays = (month, year) => 30 + (month === 2 ? (year % 4 === 0 && 1) - 2 : (month + Number(month > 7)) % 2);
returns:
countDays(11,2020) // 30
countDays(2,2020) // 29
countDays(2,2021) // 28
Solution 16 - Javascript
To get the number of days in the current month
var nbOfDaysInCurrentMonth = new Date(Date.UTC(new Date().getUTCFullYear(), new Date().getUTCMonth(), 0)).getDate()
console.log(nbOfDaysInCurrentMonth)
Solution 17 - Javascript
You can get days in month by this command:
new Date(year, month, 0).getDate();
Solution 18 - Javascript
Perhaps not the most elegant solution, but easy to understand and maintain; and, it's battle-tested.
function daysInMonth(month, year) {
var days;
switch (month) {
case 1: // Feb, our problem child
var leapYear = ((year % 4 == 0) && (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;
},
Solution 19 - Javascript
See my function and a test of it:
function numberOfDays(year, month) { // Reference: // https://arslankuyumculuk.com/how-to-calculate-leap-year-formula/ (2022-05-20 16:45 UTC)
numDays=0;
switch(month)
{
case 1:
numDays=31;
break;
case 2:
numDays=28;
break;
case 3:
numDays=31;
break;
case 4:
numDays=30;
break;
case 5:
numDays=31;
break;
case 6:
numDays=30;
break;
case 7:
numDays=31;
break;
case 8:
numDays=31;
break;
case 9:
numDays=30;
break;
case 10:
numDays=31;
break;
case 11:
numDays=30;
break;
case 12:
numDays=31;
break;
}
if(month==2)
{
if( (year % 100) == 0 )
{
if( (year % 400) == 0 )
{
numDays=29;
}
}
else
{
if( (year % 4) == 0 )
{
numDays=29;
}
}
}
//
return numDays;
}
// Test:
const years = [2019,2020,2021,2022,2023,2024,2025,2026,2027,2028,2100,2400];
month=2;
for (let i = 0; i < years.length; i++)
{
let text = "";
text += years[i] + '/' + month.toString() + ": " + numberOfDays(years[i], month).toString();
alert(text);
}
for (let m = 1; m <= 12; m++)
{
let text2 = "";
text2 += "2022/" + m.toString() + ": " + numberOfDays(2022, m).toString();
alert(text2);
}