Method Date.getDaysInMonth

Return the number of days in the month.

• Syntax Number Date.getDaysInMonth()
  
  Use this function to get the number of days in the month.
• Return value The number of days in the month.
• Examples

  To get the number of days in February 2008 (a leap year)

  // Create date
  var d = new Date(2008,1,1);
  // Output is 29
  d.getDaysInMonth();

• Resources An alternative algorithm is shown below. It is marginally slower because of the modulus computations.
  

  
  
  Date.prototype.getDaysInMonth =
  
    function(utc) {
  
      var m = utc ? this.getUTCMonth() : this.getMonth();
  
      if (m == 1)
  
        return this.isLeapYear() ? 29 : 28;
  
      // If m % 2 == 0 then if m < 8 then 31 else 30
  
      // If m % 2 != 0 then if m > 6 then 31 else 30
  
      return m % 2 ? m > 6 ? 31 : 30 : m < 8 ? 31 : 30;
  
    };
  
  

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  Source

  Unless otherwise noted all code in the JSLab Standard Library is licensed as GPLv3. See http://www.gnu.org/licenses/gpl.html for the entire license.

  This function has dependencies and will not work stand-alone. Use the download button above instead of copy/paste.

  // ************************************************************************** // Copyright 2007 - 2009 Tavs Dokkedahl // Contact: http://www.jslab.dk/contact.php // // This file is part of the JSLab Standard Library (JSL) Program. // // JSL is free software; you can redistribute it and/or modify // it under the terms of the GNU General Public License as published by // the Free Software Foundation; either version 3 of the License, or // any later version. // // JSL is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // // You should have received a copy of the GNU General Public License // along with this program. If not, see <http://www.gnu.org/licenses/>. // *************************************************************************** // Return the number of days in the month Date.prototype.getDaysInMonth = function(utc) { var m = utc ? this.getUTCMonth() : this.getMonth(); // If feb. if (m == 1) return this.isLeapYear() ? 29 : 28; // If Apr, Jun, Sep or Nov return 30; otherwise 31 return (m == 3 || m == 5 || m == 8 || m == 10) ? 30 : 31; };