Here you can find the source of daysInMonth()
Date.prototype.daysInMonth = function () { return new Date(this.getFullYear(), this.getMonth() + 1, 0).getDate(); };
Date.prototype.daysInMonth = function() { return 32 - new Date(this.getFullYear(), this.getMonth(), 32).getDate(); };
Date.prototype.daysInMonth = function() { return 32 - new Date(this.getYear(), this.getMonth(), 32).getDate(); };
dateFormat.i18n = { dayNames: [ "Dom", "Lun", "Mar", "Mie", "Jue", "Vie", "Sab", "Domingo", "Lunes", "Jueves", "Mi?oles", "Jueves", "Viernes", "S?do" ], monthNames: [ "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec", "Enero", "Febrero", "Marzo", "Abril", "Mayo", "Junio", "Julio", "Agosto", "Septiembre", "Octubre", "Noviembre", "Diciembre" ] ...
Date.prototype.getDaysInMonth = function () { var here = new Date(this.getTime()); here.setDate(32); return 32 - here.getDate(); };
Date.prototype.getDaysInMonth = function () { Date.daysInMonth[1] = this.isLeapYear() ? 29 : 28; return Date.daysInMonth[this.getMonth()];
Date.prototype.getDaysInMonth = function() { return Date.getDaysInMonth(this.getFullYear(), this.getMonth()); };
Date.prototype.getDaysInMonth = function () return Date.getDaysInMonth(this.getFullYear(), this.getMonth()); };