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Determine the number of days in a month.


npm install @stdlib/time-days-in-month


var daysInMonth = require( '@stdlib/time-days-in-month' );

daysInMonth( [month[, year]] )

Returns the number of days in a month.

var num = daysInMonth();
// returns <number>

By default, the function returns the number of days in the current month of the current year (according to local time). To determine the number of days for a particular month and year, provide month and year arguments.

var num = daysInMonth( 2 );
// returns <number>

num = daysInMonth( 2, 2016 );
// returns 29

num = daysInMonth( 2, 2017 );
// returns 28

A month may be either a month's integer value, three letter abbreviation, or full name (case insensitive).

var num = daysInMonth( 2, 2016 );
// returns 29

num = daysInMonth( 'feb', 2016 );
// returns 29

num = daysInMonth( 'february', 2016 );
// returns 29

The function also supports providing a Date object.

var num = daysInMonth( new Date() );
// returns <number>


  • The function's return value is a generalization and does not take into account inaccuracies due to daylight savings conventions, crossing timezones, or other complications with time and dates.


var daysInMonth = require( '@stdlib/time-days-in-month' );

var v;
var i;

for ( i = 0; i < 2021; i++ ) {
    v = daysInMonth( 'feb', i );
    console.log( 'In the year %d, February has %d days.', i, v );

See Also


This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.





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  • stdlib-bot
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